I used to restart my emerald game just to pick a different starter and what I experienced as a kid was that using a Treecko was too hard, using a Mudkip was too easy and Torchic was just about right---or maybe there's bias in there? (since May was my favourite Pokemon character)
Well anyway, I'll still pick Torchic for nostalgic reasons..
I'm definitely going with mudkip and torchic first. Treecko is my least favorite grass starter, and has been since my first game was Sapphire. I'll probably send one over to complete the pokedex. Mudkip and torchic, though, have been among my top favorites.
Mudkip, although I'm actually going to go full on challenge, run with what I can catch, and box the Mudkip. I want a mega Swampert in the back, just in case. I always tend to rely too heavily on the starter, so I'm breaking that habit.
I'm a little torn between which starter I want. Blaziken is my favourite but seeing as I had the chance in using him and his mega evolution throughout my entire X play through, I want something new.. Sceptile would be my second choice but I've got to admit that the mega evolutions for all three are just fantastic.
I am breaking my religious "Always Choose Water" pact, because Sceptile is my favorite Grass starter (I brake for ninjas and dragons,) and his Mega is amazing. I am really looking forward to planning my team, because I have never planned around a grass type before! Unfortunately, I can't plan my team just yet, because I like having more than one mega per team so I can handle different situations. I know it will include Sceptile and Absol, because Absol is my favorite Pokémon. I will probably have a water type and a fighting type as well, to cover Ice and Fire weaknesses (When Sceptile is in normal form.) This will also allow Apocolypto (My Absol,) to fit nicely into my team.