I went from a heavy Nikon DSLR to a lighter Nikon DSLR to several Micro Four Thirds cameras, to finally giving up and splitting my camera duties between my smartphone, and a Sony RX100. (If the RX100 had been available years ago, I am not sure I would have gotten into interchangeable-lens systems.) The RX100 has no viewfinder, has a troublesome tripod mount location, no filter ring, etc. but I am buying adapters for it that will let me use it for landscape anyway. Hopefully it will replace most of my high-end camera needs.
Along the way I also got a Canon S95 (to replace my Canon S50 that eventually broke), a Canon DSLR (no thanks, the weak warranties and no lens hoods and cheap feel of Rebels turned me off... plus Canon hasn't had a meaningful upgrade to their image sensor technology for half a decade now, talk about resting on one's laurels!), etc.
This is my personal take on all of my experiences: figure out what you actually NEED in a camera (not marketing-hype), then focus on form factor.
If you want something that will be with you at all times, a smartphone is great. Especially if you just need some quick snapshot. Smartphones are basically disposable at the rate they depreciate, so better to use their cameras than wear down the shutter mechanism on my pricier cameras!
If you want something pocketable, so that it at least has some chance of being with you at all times for situations where a cameraphone won't cut it, then the obvious, but expensive, choice is the Sony RX100. Its sensor is slightly better than Nikon 1's, and the lens is good. Retractable lens cap mechanism. Basically it's like a Canon S-series but better in almost every way, and only slightly bigger. There are some other options you might be able to shoehorn into a pocket, like a LX7 or something, but the LX7 has a lens cap which is a dealbreaker for some. (Note: ironically the LX7's lens is great and has a good sensor, vs the RX100's great sensor and good lens, so they basically cancel each other out in terms of image quality.)
If the RX100 costs too much for you and you want something small without a lens cap, then a Canon S-series is a good choice. They will be a stop and a half worse than the RX100, but be a stop or more better than cheap compact cameras with 1/2.3" sensors and slow glass. The S95, 100, and 110 are all very similar in photographic performance with similar sensors and incrementally improved lenses, but if you take videos then get the S100 or S110 which use CMOS sensors that are far better in video.
If you are willing to go above-pocket-size, you have a harder decision:
- For portability with speed and interchangeable lenses, Nikon 1 is hard to beat. It's not that much smaller than M43 when you add up body and lens sizes, but it has prosumer DSLR-grade autofocus, big-time burst speed/buffer, built-in EVF, etc. You can get thin but not very-thin DoF so for DoF fanatics this is a no-go. The V1 is nicely priced right now at $300, but it comes with no flash built-in. A nice bounceable flash is available for extra cost. Note that if you add everything up, a V1 may end up cost as much as a RX100: for a flash, a 10-30 + 30-110 kit, plus the V1 itself. You basically gain an EVF, a powerful autofocus system, interchangeable lenses, and a better flash (bounceable at more than point-blank range) for about the same money as you'd pay for an RX100, unless you get the V1 gear in a bundle deal or something. But you won't be pocketing a Nikon V1 anytime soon, either. And if you are serious about low light and sports-type photography, you will need a larger sensor size to cope with high ISO noise, so don't think this is a cheap way to get pro-grade sports gear or something, because it's not. But shots of your kids catching footballs, printed at reasonable print sizes? You bet.
- If you don't mind losing tracking speed (e.g., you shoot mostly landscapes or normal stuff, not low-light action or fast-moving sports), or if you want a better lens selection than what Nikon 1 has right now, M43 is the obvious choice and not that much bigger than Nikon 1's for bodies or lenses, even the bodies with EVFs. M43 sensors are large enough that the faster lenses in the large-and-growing stable of M43 lenses can give you DSLR-grade DoF control if that is your thing. Great bokeh on the PanaLeica 25mm f/1.4 and Oly primes, for instance. Also, M43 has the best CDAF in the business right now for single-shot. They can't track fast-flying birds like PDAF-based DSLRs/Nikon1/maybe NEX-5r/6 can, but for one-shot-at-a-time autofocus on live view or in EVF, M43 is sometimes FASTER than even high-end DSLRs. No front or back focusing issues either. Oly has admitted that they are "considering" including a hybrid PDAF/CDAF system in a future camera, but no promises.
- The next step up in size is Sony NEX. Great sensors, lens selection is small but growing. The main problem with NEX is small bodies with big lenses. It's even less pocketable than M43 and makes for unbalanced setups at longer focal ranges. The lens size issue goes away if you use pancake lenses but there are few in number and the optical quality is OK but not great. And if you want a viewfinder or flash, that's additional size and weight. However, NEX-5r/6 have PDAF, so if you want PDAF but don't want the bulk of a DSLR but want a sensor larger than that in the Nikon 1, NEX is currently the way to go. I have heard mixed things about it and suspect that they can't match the speed or accuracy of a Nikon 1 or prosumer DSLR.
- Samsung NX appears to be roadkill but if they ever wake up they can be a true threat to NEX.
- Then you have the traditional DSLRs and these vary greatly on size, sensor size, viewfinder, etc. but have great compatibility with all sorts of glass (new and old), accessories, etc. at the cost of size and weight. If you try to match feature-for-feature, you will find that DSLRs are often more bang for the buck than mirrorless counterparts; a mirrorless camera would have to have PDAF, viewfinder, and big sensor, and that means NEX-6 which is close to $1000 whereas you can find a D3200/D5100 for a LOT less money. But bang-for-buck means little if the gear is so bulky that you don't carry it with you. "The best camera is the one you have with you at the moment." A pocket camera thus beats a DSLR, if you would otherwise have no camera at all because you left your heavy gear at home because it was a pain to haul around.
So there you have it. Figure out what you NEED, then get the smallest camera system that meets that need. If there is a dealbreaker/maker like EVF or PDAF then that may sway you. I can't understate how important size/weight is in the long-run. I'm not an old geezer or anything, but I really do NOT enjoy carrying DSLR and DSLR lenses with me on backpacking trips and such. At Best Buy you do not gain a full appreciation for certain things, such as how heavy things weigh. Don't go "oh well they weigh about the same anyway." Sure they do--if you are carrying them for short periods of time. But you don't truly know how much something weighs until you lug it around at Disneyland or up and down a mountain or whatever. So that is why I recommend figuring out what you NEED, and then buying the smallest camera that meets that need.
Also note that over time, electronics will continue to improve, so whatever form factor you buy into will only get better and better. 10 years ago you pretty much had to use a bulky DSLR to get good-quality photos, but electronics have vastly improved to the point where a RX100 or Nikon 1 performs similarly to the early DSLRs, at any given paper print size. (This is sort of like how a modern iPad probably has the computational power of a laptop from 10 years ago. Maybe more.)
Finally, note that lenses and other accessories like flashes are usually in proportion to sensor size, so if you plan to carry multiple lenses then you should take that into account, e.g., you can't compare just the base camera and kit lens when comparing weights, unless you are never going to carry other lenses, or spare batteries, or filters, or flashes, or remotes, or tripods, etc. You should add up the weight of the entire kit and compare that way. Things will vary depending on exactly what is in your kit. Example: mirrorless eats batteries WAY faster than DSLR so factor in the additional expense, size, and weight of carrying spare batteries for mirrorless systems, which takes away a bit from their weight advantage. But you do gain a bit of weight advantage back if you go with smaller cameras, as that allows you to use smaller tripods. Etc.