Which Jedi class is the best to choose?

I think it depends on your attack preferences - if you're using Force powers the most, then Consular; if you just use melee, lightsabers, or ranged weapons more frequently, then Guardian, if you can't decide and wanna split the difference and have a balance, than Sentinal...just a personal prefferance really.

I think it's easier to START as Guardian, and learn the combat. Then choosing Consular on the next play through and using force powers.