Going by "by gym 1", HGSS has a lot - because there's not just what's in GSC (early route pokes, the sidepath offering Geodude/Jigglypuff, the grass in Crystal west of Violet City (Growlithe, etc) and the patch south of it (Mareep, Hoppip, Ekans, etc), Unown, etc - but there's also the Pokewalker. Whole bunch of Pokemon there.
B2W2 also did a good job, certainly. Much better than BW which imo was the worst of the bunch.