Besides my own team number which has my lucky number (27) and The Intimidator's number in it as well (3) I would have to pick
18 - Not so much that it is the legal age for a few things, but that an Electric Car team I am/was on in College has that number.
27 - It's my lucky number, and I want a shirt from that team as well!!! Team RUSH I believe it is?
Team 44 - My favorite NASCAR Driver drove that for a while, with the coolest (die-cast) car company as a sponsor. - But unfortunately the team does not exist anymore - meaning no shirt trading.
Team HYPER's number - The obvious reason

As for High numbers, you have to love your own millenium team.
1237. They are (kind of) local to us. We competed with them at the NYC regional their rookie year.
edit: How can I forget a number... Well I did..
79 - Just cause that is the year I was born.