I get the the bit about Sal, but there is always the Deputy build, which makes Sal require skill instead of just Unkempt Nozzling your way through each map. I have one of each at 72 and/or in the process of peaking, and the order I started them was Zer0, Axton, Gaige, Krieg, Salvador, and Maya. To be fair, all of them require a fair amount of adjustment, and had a learning curve before I got comfortable with each one. Some things I noticed on my way:
- The longest AS cooldowns are the pet classes (Axton and Gaige) and Krieg (until you get Release the Beast or get comfortable with self damage)
- I thought Salvador would be easy and therefore felt like the game was smacking me around in the early stages.
- Zer0 appealed to me the most, which was why I started with him, but probably required the most work to get decent with.
- Maya was probably the most forgiving of my impatience and lack of finesse.
- Krieg is probably the most fun you can have mobbing once you get Release the Beast and Bloodsplosion.
- Gaige can either be easy to play or hard depending on how you build her.
TL;DR: there are no bad choices (even Sal ), maybe the best way to decide would be to watch some game play videos and see what looks like the most fun for you.