I do mostly 3-gallon batches. For primary I use 5-gallon carboys that were intended to be secondaries for 5-gallon brews. They're (relatively) cheap and every home brew shop sells them. I do have proper temp control, and don't really do brews notorious for blow-off like RIS's and Heffes, but I have never even come close to a blow-off with that setup.
I use the 5-gal plastic Big Mouth Bubblers, but the old, barely adequate, lid design. I think the new lid is even worse, so I'm not sure I can recommend them. For secondary (which I almost never do at this point) Better Bottle makes a square 3-gallon bottle; 2 can fit perfectly side-by side in my fermenting freezer, meaning I can fit 2 secondaries AND a primary.