So, a few more thoughts on the unlocks and stuff before most of you get the game and find out for yourselves, so you can have a good idea where to prioritize. First the perks:
Tier One:
Lightweight - Always a good choice. Add it to a LMG class to counter some of the mobility loss. Or better yet, add it to a SMG class to run around super fast, which helps with escaping, and really helps with capturing objectives and the like before anyone else gets it.
Flak Jacket - Very useful in objective games IMO. You know, the ones like domination or demolition where people just randomly chuck grenades at the objectives, this will get you a lot more caps. Unfortunately, while a nade wont outright kill you, ever, an RC-XD blown up right under your feet still will. It'll protect you from more distant RC-XD blast, but IMO it should protect you 100% of the time. It doesnt. Pro makes you immune to fire and resets the throwback timer, but its pretty hard to unlock as it requires tossing back quite a few grenades, something you dont get the opportunity to do. But it would be awesome to lay down some napalm and cap a objective in total safety surrounded by your flames.
Scavenger - Useless IMO. You start with 3 extra clips instead of 2. You rarely run out of ammo, unless youre a real punk camping son of a bitch. It also wont refill noob tubes, and if you were planning on that, you can also die in a fire. Nor will it replenish equipment like claymores, not as if you'd crawl out of your hole to pick more up if you were using them anyway. If you need more nades, get warlord pro.
Ghost - Very useful to counter the near ubiquitous spy planes. But you really need to unlock pro as soon as possible to hide from choppers if you plan on using it a lot, and this requires exposing yourself quite a bit as you need to shoot down 30 KS from the sky using a launcher. Sam kills wont count. You also need to get 150 suppressor kills (simple), and destroy one sentry. Destroying that sentry is harder than it sounds, cause NO ONE is using them ATM, and youre not invisible to them. If you hear a sentry inbound, find it and kill it ASAP.
Hardline - My personal favorite, especially for TDM. Its mainly useful for getting low KS such as spy planes, sams and the like. One less kill for a 3KS is a 50% improvement, and thats major. With it on, you alone can basically keep your team's spy planes up near 100% of the time, and combined with the 33% improvement to getting counter SP and SAMs, you can keep their KS and radar down most of the match. Havent got pro yet as it requires you to give away 10 packages, which is easier said than done.
Tier 2:
Hardened - More useful that you'd think, since gun battles tend to be more protracted, especially behind cover. It basically allows you to shoot people out of windows much easier. Really good for an LMG or semi-auto gun. The pro version doesnt add much. The reduction of flinch might marginally help a bit, but its not huge. The added power of bullets to shoot down KS is still useless, as shooting down stuff with a gun is still more trouble that its worth. Get a launcher or SAM for that.
Scout - Utterly useless, as sniper rifles in generally are now totally nerfed due to the anti QS fix. Skip it.
Steady Aim - Good for a run and gun SMG class, but only with the heavier SMGs such as the MP5 or AK74. In that case you'll prob want to combine it with dual mags for a faster reload, since SoH will be locked out. OTOH, The small clip machine pistols like the MAc-10 and PM63 really dont need it, they fire great from the hip already. What they DO need, is extended mags and sleight of hand, if thats your play style.
Sleight of Hand - A staple, and one of the best choices in this tier. It really feels like ADS is already much faster stock in this game than in previous CoD, and with Pro its god damn near instant. The faster ADS also doesnt work with sniper rifles, and strangely, while it does work for the ACOG with the WA2000 (and probably other SRs), it doesnt work with the Dragonov ACOG. I suspect this is a bug, since it doesnt make sense. Not sure which they intend, but I think they should allow you to use it with all SR + ACOG.
Warlord - Of limited usefulness, for many reasons. You cant combine it with under barrel attachments, so out goes the noob tube, flamethrower and masterkey, the only one of which is useful anyway is the noob tube. You also dont want to use it with dual mags, as you'd be better served by just using SoH and the other attachment. This leaves it to use with a combination of sight, suppressor and extended mags. Sights are much less useful in this game since iron sights are generally fantastic, and extended mags are good on LMGs, but I recommend SoH instead of them in virtually all other cases.
Tier 3:
Tac Mask - Completely and utterly useless. Replace it ASAP. No one uses nova gas against you, and thats all the stock protects against. Unlocking pro - which protects against flash and concussion, requires you to get 20 kills against people youve gassed, 20 against people youve flashed, and 20 against people youve stunned. Its nearly impossible unless this is all youre trying to do for the first 30 levels. Gassing people is particularly hard. Its just not worth it unless you are a god with the flashbang.
Marathon - Might be useful for some objective matches, and the stock version gives you about as much extra sprint as extreme conditioning from CoD4. But running around leaves you open, so unless you've got steady aim pro, you're probably better off just not running and using lightweight instead.
Ninja - The stock version is, as the other guy in the video said, damn near useless. The sound engine in BO is much more sophisticated than in IW games, where sounds around corners are muffled to the point where you'll rarely hear footsteps coming around a corner. Even with a good headset, you only hear them if theyre right in front of you, and at that point you'd better already be shooting. I'm one backstab away from pro which I suspect may be very useful, not so much to make you completely silent, but to make other footsteps louder to the point that it might help to actually hear them. Otherwise, ninja is probably best left to those playing S&D.
Second Chance - Havent used it much, as its really only useful to randomly steal back a kill, a kill that you might otherwise have gotten if you had a different perk. No one has the pro version, and I wouldnt trust my teammates to actually revive me.
Hacker - Right now, pretty useless as not too many people are using equipment since none are unlocked from the start. But given the limited usefulness of the other Tier 3 perks IMO, its still a very solid choice, and will probably become more useful as time passes by.
A few more quickies:
Use extended mags with LMGs, for sure. While for ARs and SMGs they provide a 50% boost, for LMGs, they double the clip to a drum mag. Makes them more like proper LMGs.
The motion sensor is suprisingly useful in objective games such as headquarters or domination. You place it down, and it blinks red on the radar for anyone that gets near, including those using ghost. You need hacker pro to subvert it, and NO ONE is using that.
The decoy is awesome, but really annoying to your team if not used properly. You get two, that you can throw pretty far. It blinks green on you and your teammates radar, red on the enemies. It has a fairly recognizable sound of fire a few shots, reload. The problem is that your teammates and yourself just hear gunfire, and it bugs them out. Its really annoying when people start throwing them out randomly. Its good for really only two things - one, if youre camping, throw it way out, and wait for someone to come to you. But remember, you're also attacting attention to yourself. Where it really shines is in objective games like headquarters or S&D. Cap or plant, then chuck them way out in the distance. It confuses the sh*t out of the enemy, making them fearful of approaching and defusing, adding that precious time that you need.
The camera spike is cool for getting vision out of another window if youre camping, but I think you're better served by a claymore guarding yourback.
Also, if youre going to use a RDS or Reflex, consider using blue as the color. Its much dimmer than the other ones, makes it much easier to see through your sight. Green in particular is god damn near opaque. The three dot predator shoulder laser type recticule is also a good choice, as it keeps the center kill zone completely clear. The circle is WAY too bright. The standard tiny dot is really one of the more solid choices.