Someone mentioned those guns that actually heal you as well before, thanks for reminding me. I must have missed them on my first playthrough, they would be a massive help alright, the grenades that steal health are the only thing keeping me alive (barely!) on UVHM.
I will look for rubi and grognozzle, I think I might have had the lady fist before but I must have gotten rid of it, I didn't even know that it healed you! Are those all the weapons that heal you or are there any more?
Lady Fist doesn't heal--it's just a really good high crit gun, and is great for Sal's main hand. You get it as a reward doing the TK baha mission in the Old Firestone area...dang, forget the name of that map.
Be sure to turn the quest in to the niece, and not Hyperion--that mailbox is next to the bounty board that gives you the quest.
All Moxxi weapons heal. it's a hidden trait that you don't see in the gun card.
Grognozzle is only obtained by certain shenanigans (unless you played during the month long bounty event several months ago, when it dropped from the legendary golem in Tina's DLC). It's a mission-based item that you get while doing claptrap's mission in the mines of avarice in Tina's--the one where you have to get the dwarves drunk and smash them--I think claptrap wants their beards. Start the mission, but never turn it in. Grog will stay in your mission slot, so it won't take up an inventory slot. If you do co-op, you might lose it, though. I forget the specifics, but it can disappear. and various players hate people that use it--consider it cheating.
Grog has the strongest healing--something like 54% of damage, I think. It's nuts. There is also a chance that when you swap to it, you will get "drunk." This gives a little wobbly animation, decreases accuracy, but also doubles...or triples or quadruples? your bullet output for ~4 or 5 seconds. So, same ammunition cost, but up to 4x damage. You can swap in and out until you see the effect, then swap to your main gun and blast away. As you can imagine, this makes certain guns godly.
You get Rubi from Rakkaholics anonymous, the mission from Mordecai after Bloodwing is killed. Just turn into Moxxi (Mordecai will give you a shit gun). Here, you will probably want to spawn a good version, if in UVHM. When she shows you the gun, just alt F4 to close the game without saving. reload, do again until you get what you want. I guess that only matters for Sal, though, where you really want a slag variant. For all other toons, you should be slagging in other ways, and Rubi is just used for healing. Outside of Grog, Rubi is the best healing Moxxi game in the game--I think it's 12%, and all other legit Moxxi weapons are something like 2%
Rubi is all you need, really. You can get through UVHM and digistruct without grognozzle. Just remember that moxxi guns heal you for any type of damage. Most people will swap to it, toss some Tesla grenades, or maybe a now-buffed Fastball or those other legendary mirv grenades (you get from Torgue machines--forget what they are called), and just watch the redbar go up. Just remember to keep the gun in-hand as the damage is being done. I'm not sure if Deathtrap damage counts, though.
If I had to rank them, in terms of healing and general effectiveness:
Rubi (because it is "legit," and has all variants. Healing can still restore all health within 1 or 2 seconds at OP 8 mobs)
Grognozzle (godly healing and godly damage effects; but it is not "legit" and has no slag variant)
Heartbreaker (very good damage, always fire, very fast fire and reload. This can heal you very fast when blasting things in the face. It is quickly out-leveled though. I suggest gibbing it up to an appropriate level. I think you want critical variant, or the one that adds an extra bullet. forget that label). You get this one for recovering Marcus' porn stash in Caustic caverns--he gives you this mission after you return to the now-floating Sanctuary. Just turn in to Moxxi instead of Marcus--which brings up another point: Whenever you have such a choice, always turn in to Moxxi.
Creamer (damage is kinda poor, but people like it for getting out of FFYL, because you come back with something like 75% or more health. it's very situational)
Bad/Good touch (Bad touch is pretty good damage, but is easily outclassed by many other SMG with larger magazines and better accuracy. Plus, you can only get one Bad Touch on your toon, throughout all playthroughs, so you might likely get it in normal mode and then you're screwed. --tipping Moxxi something like 100k+ before she will give it to you. Good touch she will randomly give to you on any type of tip. multiple times...I think)