In my humble opinion I would rate the Starters as:
R/S/E
1. Swampert - Only reason I wouldn't choose it is cuz there is million water types, but it only has one weakness, to a type that is almost non-existant in those games, and it learns a ton of good attacks, to go with it's good attack stat.
2. Blaziken - Good Combo attacker and has good speed, also pretty much the only Fire in those games, except Camerupt, and Magcargo I think... neither are very good.
3. Sceptile - Just never really worked out for me, don't know why, it looks good on paper.
FR/LG
1. Venusaur - Arguably the best Grass type in any game, it also isn't a super common type. If I don't choose it a descent alternate is Victreebell
2. Charizard - Fast special attacker, and fire is hard to come by, but a Ninetails or Arcanine will work almost/just as good
3. Blastoise - Quite possibly the worst starter ever, yeah defenses are pretty good, but it is slow as sin, and neither of it's attack stats are good enought to make it a real threat. Not to mention all of the good water types in those games. I.E. Gyrados, Starmie, Lapras, Omastar, Vaporeon, Dewgong...