Red being the first one said would automatically make it the most popular one (it's just the way it goes). Which means technically, for trades, you'd be better off with Blue for version-exclusives, since more people will be wanting the ones you have.
Arbok = Sandslash
Victreebel > Vileploom
Arcanine = Ninetails
Persian > Primeape
Magmar > Scyther > Electabuzz > Pinsir
So I guess I prefer Blue, personally. Although I did skip Red/Blue and go straight for Yellow.