Buy a rifle that is ready to compete. Forget the cheap ones that you have to add upgrades to make it perform because, chances are, it may never. For FT, .177 cal is the only choice. I've seen the BSA perform very well. The AA rifles, whether the 500 or 510 are great choices too. It would be advantageous to get a rifle that is regulated too. Don't forget that the shooter is the one who makes the gun perform. You can buy a $3000 rifle, but that won't make you a winner. Maybe a whiner.
Look at the field target match results on the various forums and see which rifles the shooters are using. That's a good indication of what is successful.