Well RT is generally for larger troopers but you can't go wrong with AP/TE2/TM. I'll let someone that knows more about TM armor chime in, but I wasn't aware that it was larger armor.
ABS vs Styrene, we have several of those threads around. Styrene will last for years of trooping just like ABS. The difference is you have to paint styrene and the quality of the paint job is probably what you are seeing over ABS. If your worried about the styrene cracking, just troop normally and you'll be fine, but you can't play football in it like you can with FX armor.