Any plane with cannon. 1 single hit in the pit on the hit and the splash damage will destroy it. If you fire an HE rocket you can be further away and still destroy the gun. Set your cannons to 400 yards convergence, one quick burst (as short as you can make it), and then move on to the next gun. The fighters with the center line 20mm is nice, you only have to worry about trajectory and not convergence.
Using MG rounds (.30 and .50 cal) you need to get a direct hit with multiple rounds to destroy the gun. It can be done but it is not as easy to do. I routinely de-ack towns in two passes using a cannon equipped fighter. I'll use rockets as well, but either way... use something with HE so that you do NOT have to get a direct hit.
Cheers.