GSD. Easily the worst Gundam series ever. This one doesn't need any explaining for anybody who has seen it, besides which, its many many faults have been pointed out and debated upon in these forums more times than any of us could ever accurately remember.
Wing. As RX-78GP04G Gerbera pointed out, the "Invinceability Factor" as well as his other points. GW got me hooked on Gundam, but I'm not going to call a not-good/bad series good just because it was what started me on the franchise.