To follow up on what Plazus was saying the 38L is the best for hauling ordnance, it carries more with the smallest drag penalty once that ordnance is expended. The J/L weigh more than the G does but have more powerful engines, the extra power will help vertical performance, and they fight uphill better than the G does. Some people believe that the J handles better than the L, I can't speak to that directly as I never flew the L very much (I just like the skin options on the J more). The J and L have the same engines, the same airframe and the same weight in game, the L has the boosted ailerons which will help roll rate at high speed and the dive recovery flaps (not dive brakes), as a result the performance is very similar.
These days I fly the G for the most part because I think it looks better and I like the history associated with the F-H models more so than the later J and L series. The G carries less internal fuel so be aware that it will have shorter legs for the same fuel load than the other two it also lacks WEP so vertical performance isn't quite as good either, most will say that it turns better as well although I'm not sure how true that is anymore since an error was found awhile back and a few hundred pounds of weight was added as a result.
