Siren is probably easier to start with than Axton, I think.
I'll have to disagree with you on this one I'm afraid.
Simply put: Preparation. You can have it from level 6, i.e. your 2nd skill point spend, which gives you health regeneration. Maya is lacking in any health regen skill, so you'd have to hunt down a class mod or something to get the equivalent. I had a short play as a level 8-9 siren last night, and kept getting put down no end, because I kept finding myself with naff all health!