My favorite starter is Treecko! It was awesome back the and it's even more awesome now that Sceptile got a mega evolution! It's sad though that it has always been nerfed or hindered in many ways, resulting in it not being as useful as it should. For example, on top of a terribly shallow movepool, it got one of the best moves it can learn, Giga Drain, at level 53 and ONLY if it didn't evolve! It has many good things going for it too though! It has a really useful ability (Unburden) and, as a Sceptile, it already has high Sp. Atk. and Speed stats, so after that boost, you are good to go. You can also change the strategy a bit and go with Mega Sceptile, which has greatly improved offensive power and speed as well as a nice Dragon typing, with a Discharge partner in doubles, getting a Sp. Atk. boost every turn thanks to Lightningrod!