It is based on personal opinion but i recomend yellow as it allows you to get all 3 starter Pokemon without trading and has more features than red or blue
In the safari zone or trade one from blue.
you can not catch a pikachu in yellow, but you can get it from blue or red. The only pikachu you get in yellow is the one you start with.
You can't, get one from red, blue or yellow.
One can trade in Pokemon Yellow via link cable. Two Gameboy consoles can be connected via link cable and Pokemon can be traded across Pokemon Blue, Red, or Yellow.
I don't think there is a yellow elephant Pokemon... There's a blue one named Phanpy and a gray, dangerous looking one named Donphan.
there are a lot to mention but I'll give some. in Pokemon Yellow you can have Pikachu, Charmander, Bulbasaur and Squirtle all at the same time where in Red and Blue you can only have one. Meowth is not wild in the Yellow version but can be caught in the Blue version.
You can't get one at all in Gold. You'd have to trade one from Red/Blue/Yellow.
The only way to obtain a Kabuto in Pokemon Crystal is to trade one over from Red, Yellow, or Blue.
You must choose it as your starter if not you need to have red or yellow trade you one or receive one from Pokemon stadium as a Pokemon present.
Its weird but you can't catch articuno in silver get one from red, blue or yellow.
you don't catch articuno in crystal but you can get one from red, blue or yellow.
The only way to get an Articuno without GS is to trade one from Pokemon Red, Blue, or Yellow.