Haven't made a Salvador yet, but Axton with skill points pumped into turret upgrades is pretty unstoppable. I think the turret is designed to supplement a 4-person team, so it's ridiculously powerful solo.
But seriously, all of the characters can easily solo the game as long as you know what you're doing when you build them.
This or melee/gun hybrid zero. Maya is excellent down motion with sweet release, and one other skill, can't think of of, kill skill where she heals x%. Melee/gun hybrid zero with even a low level rubi can provide massive health regen. at level 50 with 50 rubi, deception + last second melee heals me from >100hp back up to 55k.
Also the nice thong about rubi,I have learned, is any kind of damage you do, if its kunai, shooting, melee or even grenades, you will get health back due to rubi's red text.
as for axton,salv and gaige that's a different story. I haven't touched them yet. --- Xbox 360 Gamertag: DoS Paper Clock Will Farm For Food.. </3
Depends on how good you are with games like this, as I've seen some people become devastating with Motion Maya. However, Axton and Gaige are two good places to start since their abilities create other entities on the battlefield. The Gunzerker's alright as well, especially because of the ammo regeneration, but you'll encounter difficulty with some bosses where Axton and Gaige won't (to the same extent).
NOTE: I main Axton as my solo character and the Gunzerker as my split-screen character (I haven't played online because I just enjoy playing with friends). I haven't even tried out Gaige yet, but her skills (and the praise she gets) lead me to believe the above.
I've leveled a melee focused zero and I would not recommend that as a first character to run through the story...unless of course you really like playing that way. It is doable but I still had some issues here and there even with decent gear from previous playthroughs.
I think most people, as mentioned above, would say that Salvador, Axton, and Gaige are the most forgiving for new players but that doesn't negate the effectiveness of the others...just relative ease. --- Fact because it's science. ==============================================