FFIV - Kain/Cecil/Rydia/Rosa/Yang
I'd add Edge.

FFVI - Locke/Celes/Terra/One of the Figaro brothers
I'd surely add the other Figaro brother

FFVII - Cloud/Tifa/Nanaki
I'd add Vincent.

FFIX - Zidane/Vivi/Garnet/Steiner
I'd probably add Freya.

FFX - I absolutely love the party switchings.

FFXIII - Lightning/Hope/Fang
I'd probably add Vanille because she's a much better Saboteur than Fang, but Fang is better in general and makes a good team with Lightning and Hope.