I think this has become "opinions: the argument" now, but Decidueye is a much better candidate for a Smash character than Sceptile. Zoner, Ghost, interesting visual design. Probably the best Grass starter ever (imo obviously). Just has much more personality and flair to its whole design than Sceptile.
In any case, I believe it's the best candidate for a Grass starter. It's decently popular and it has the added bonus of relevancy to the current Pokémon generation.