Best Tramps for jump training

I really want to learn inverts on snow next year, so far on tramp i can do most of the rotations (/claim), but id really like to be more comfortable with them. i sometimes can get out to places like skyzone, but i want something to practice on everyday. One of my friends has a rectangle trampoline which is scary because ill sometimes catch my feet on the net. So id prefer if you guys could tell me what tramps you like for the price and aren`t rectangular. Are there square trampolines out there for good prices? also is the difference between a 12 and 14 ft tramp alot? thans newschoolers