I was in the same boat a week or so ago, and was really befuddled on what I should go for.. Finally I settled on Ramos because everything seems easy...
tactics are straight forward (either get a crap ton of spiders and summon like mad, or get some beatstick elites and summon like mad) models looked very easy to paint (not a lot of wild paint schemes or too much detail, and a lot of repetitive models so painting seems more easy than any other master) I figure Ramos will get me into the game, and sharpen up some badly neglected painting skills (haven't painted for like 12 years), then once I feel confident in rules and painting, I plan on taking on a levi or gremlins crew after Gen-con (much more intricate tactics, many many more options... levi is insane with options... )
I really don't select out of fluff, (though the green ones seem pretty funny in both fluff and rules)
I admit I'm a bit of an ego manic, I greatly prefer winning and basking in my infinite awesome over losing. Ramos seems to have a fairly proven track record with a rinse repeat sort of game play... perfect for a starting player, nothing too tricky or requiring too much set up or pre-planing (throw a Ramos crew together and it should work with only a smidgen of considering the enemy master's play style ), a lot of the other masters with burning army list/schemes, hard to grasp model rules, very specific ways for the model to survive long enough to afford the SS cost and what not seem like far reaching tactics that would take a while to master. Against experienced opponents that translates to a lot of losses and not much awesome basking.
so I'd strongly suggest (from one new player to another,) find a first crew that you think you can have success with. Forget the look of the crew, the fluff, and pretty much everything else and just select something following K.I.S.S. that you think you can paint fairly easily, learn fast and start winning with soon.
you'll be much less likely to have fun and keep playing if you select a really hard to paint crew that takes forever to get finished, then takes a lot of losses and facepalming before you have an even chance of winning with.