IIRC a lot of the RBG sprites looked way different was because they came around before the Sugimori art or the Anime. I think the 1st pic of Pikachu is the best, I loved him when he was chubby :3
While Gligar looks really similar to when it debuted, it's color seems to change every generation.
Me personally, I love the 1st Gligar one just because it looks so vintange and pretty Awesome in general. Also I like the 3rd Pikachu one because it looks like a big yellow-outlined ball.
Typhlosion front sprites haven't changed much apart from big jump from 2nd gen to 3rd gen.... but back sprites then again changed very lot.... also shiny colors were epic in 2nd gen. Notice ears getting bigger every gen lol. They sort of made 5th gen back sprite little dumb looking
In my opinion, Zapdos made some very nice improvements. It's strange that a first, Zapdos was at first a very light yellow color, changed into a neon yellow, then got darker..., But still, Zapdos is awesome.