Shooting a semi-auto gun is more fun for me. That's why I have one. I can shoot into my bullet trap in the basement and not spend a lot of money for ammo while doing so. It's good practice too.

But, you wouldn't really need a semi-auto pistol for a trap line. If you bought a semi-automatic pistol for that sole purpose you'd probably be spending more money than you'd need to. That is, if you buy a good quality one. I would also go with a revolver. Less things can go wrong with one. Keep it cheap and simple.