Revell Germany and Hasegawa make the best models. minicraft makes some good ones, and Airfix makes.... fixer-uppers.
Minicraft's best is the MD
-80, however, the 737s are also good. Rumor has it that Minicraft is/has updated their 777 and 707 kits. I believe the updated kits will carry some sort of badgeing on the box, so it'll be obvious. I'd almost be inclined to suggest minciraft for a first model, as they are generaly simpler than the revells (and much easier to get a hold of a a reasonable price than the hasegawas). Both the 737 and MD
-80 are easily avialable in diffrent schemes and have no real noteable fit problems. All of the revells are good kits, though the 747s have some minor problems. I just built one of their Fokker 100s, with the goal to finnish it quick insead of letting it gather dust for years. It went toegther great, and except for the pain in the hindquarters of a copckpit would make an excellent first model.