I'm playing a human psi warrior who focuses in mounted combat. It is a great deal of fun. I picked up leadership and convinced the dm to allow me to take the griffin levels from savage species to start off my cohort.

Psi warrior is very versatile; it allows you to do a lot. If you want to go more nature warrior oriented the claw based powers are a lot of funs and can lead to you healing a great deal of damage back when you hit someone. If you want to go battle field controller you have enough feats and powers to pull it off.

If you want to go heavy defense I would suggest monk for a level to get wis to AC then pick up inertial armor, precog defense, and a few other powers to really bost your AC.

Another option is to go heavy hitter with a two handed weapon there are a great deal of self buffs and as mentioned earlier prevenomed weapon is very useful.

The last psi warrior I played (wasn't that optimized but was fun) was a paladin of freedom 2(varient in unearthed arcana) psi warrior8/ illithad slayer 7 who was on a holy mission to rid the world of Ilsensine and his mind flayers.

Just don't forget to pick out pounce as soon as possible getting those extra attacks after a charge or move action really lets you shine compared to the other melee based classes at that level .(with the exception of 1st level barbarian substitution cheese)

Overall Psi Warrior is one of my favorite classes and I hope you enjoy playing it.