Since I'm fire biased and always liked Torchic's evolution line, I chose Torchic although I really want to go with Mudkip as I'm already liking Mega Swampert tbh. That, and it'd be fun to try something new this time around but depending on what I get but I'll leave it at that. I didn't get Pok?mon X/Y event Torchic though so yeah, may end up getting that.
I always use water type as my starter apart from Kanto region and Mudkip (+evolutions) is one of my favorites. I'm most likely getting Mudkip but I grew to love Torchic/Blaziken because of the XY event and it was my first time having it in my party. Was amazing. I'd probably have troubles deciding but I've decided on Mudkip since I can just transfer Blaziken over, maybe.
I love all three so I can't really choose one. I always changed it up when I restarted the games, although I gotta say, Swampert will certainly make the majority of gyms easier for you, and Blaziken is great in the Elite Four.
Tough choice between Treecko and Torchic. Treecko is my first starter and I like Sceptile's design, but Blaziken is pretty cool too especially with Speed Boost.
I chose mudkip cuz he's a cutie and looks like a beats in his final form. But on a side note, I'm just wait for the stupid mudkip memes to resurface from the deep depths of the internet.
Despite saying this, I actually ended up picking Treecko. It got to the point of making a decision, and I decided that I didn't just want to go with the same starter I used back in the original Sapphirealthough I did that with Silver & SoulSilver. Treecko is actually my least favourite (and least played) of the three but I had the urge to pick it. No regrets so far.