It really depends on a lot of factors - the type of gun, weight of the gun, cyclic rate, muzzle attachments, caliber are all factors.
That said, .22 MGs are probably the most controllable. The American 180 (and Yugoslavian MGV176) fire .22 at a rate of about 27-30rds/second depending on the type of ammo. At that speed and with the weight of the weapon, yuo really don't reel the recoil of each round - its more of a very gentle push against your shoulder. Most people consider the .308 G3 to be among the most unpleasant to shoot because of its recoil, but I don't mind it at all. It is difficult to keep on target if you try and dump a 20rd mag all at once, but if you shoot in 2-3rd bursts, I find it pretty reasonable. A friend of mine has a Vito Cellini brake on his G3 and that tames the recoil considerably. Also in the 308 vein, you'l often hear that the M14 has very stout recoil also, but the Italian BM59, although quite similar to a M14, is easy to control due to the brake.
Generally the larger the caliber, the more recoil it will have. The heavier the gun, the less recoil. If a gun has a muzzle brake rather than a flash supressor, you'll probably feel even less recoil.