main is a marauder, valor rank 66, I switch specs every few weeks to keep it fun. You should try playing each to see what you like. they are all viable but best usage can be situational.
Anni is pretty good 1v1 spec, the self heals are great when you don't have a healer. Having the snare spec is a 100% must though, otherwise your life will be difficult because it's the easiest spec to kite/run from. Not gonna say much else about it, I'm sure you've heard enough people wax poetic about the spec.
Rage is a great team fight spec. I actually used to have a really easy 1v1 rotation pre 1.2 with 9 sec cd smash but now that it's 12 sec, my rotation is messed up so it's been a little bit harder bursting people down (even though damage is buffed 20%). The smash crits rack up a huge amount of damage in team fights and the more people you catch with it, the easier it will be to rack up damage.
Carnage can be interesting and I can't really explain it that well because I think it's something better understood by getting a feel for it. Some simple examples of use though are the roots help a ton in huttball because they ignore resolve and you have 6 seconds of it to help your team down the ball carrier. Also, 1v1 situations against other melee heroes allows you to outplay your opponent; sometimes easily if you do it right. Play in-and-out with deadly saber to hold them there while you scream/vicious throw from afar.