12 Gauge is what I always used when I shot trap alot. My uncle who got my into it bought himself a cheap single shot to see if he liked it, which I then used to see if I liked it. The problem was that because it had so little mass it beat the hell out of you, even with the AA Extra Lights.
Speaking of which, not sure how much you shoot but If you're looking to try it out and have a lighter weight gun I'd recommend buying the Winchester Xtra light loads, or the even lighter "low recoil/low noise" shells (I beleive these are the lightest production shells you can buy) don't buy anything too heavy, once you put 100+ shells through it in an afternoon you'll feel like you've been clubbed with it, and that's not fun.
Good luck.