My old mount just died and I'm looking for suggestions for my new mount and my friend says I should get a T-Rex as my paladin mount I don't know about that.
if you want more than a horse or camel you need to check with your GM. That's the official rule.
If you take the monstrous mount feat, you can pick from a few more fun options.
the GM said i could get anything on the druids animal compaion list(non-plant) if I got the monstrous mount feat.
Mechanically, the best choice is usually a big cat with pounce. There are other fun ones though, like a large wolf, or a roc, or various dinosaurs.
If you ride your mount into combat and have associated feats, go Triceratops. Get them special barding/armor for more intimidation.