I want to know who would be the best to start out with?

It doesn't matter who oyu start off with, all three pokemon have their ups and down sides.

Well basicly, there is no best starter. If you want to beat the first second fifth gym and the elite four easier, you'll coose torchic. If you want lots of hm's and beating the first third fourth and seventh gym easily, you'll choose mudkip. If you want awesome speed and beating the first third and sventh gym and a sort of easy elite four, you'll choose treecko. It also depends on how you want to beat team magma. If you want a not to easy but not to hard challenge, choose torchic. For a challenging battle, choose treecko. For an easy battle, choose mudkip. And if you want and easy groudon battle, choose mudkip. For a semi-easy battle, choose treecko. For a challenge choose torchic. All the starters have different statistics. Mudkip can beat torchic, torchic can beat treecko, and treecko can beat mudkip. But it all depends on the moves you teach them and wich one is YOUR favorite. or just follow the steps i just gave. It's all up to you.

They all have good and bad points,for example marshtomp makes it harder to beat your rivel because grass is super effective againts water and ground,but makes it easy against a lot of gym leaders.

No matter what anyone says mudkip is the best pokemon to start off with as water pokemon have more HP and defense.

Well... They're all really cool, but I think its just a matter of preference. I've got Ruby and Sapphire. I used Mudkip in Ruby but my fave is Torchic. I used that in Sapphire, even though it has Team Aqua in it. But I did fine. So you can actually pick a starter pokemon like Torchic in Sapphire or Treeko in Ruby that has a weakness, but once you spend more time with it and get its level up, it will adore you plus be very powerfull. So they're all really good, just pick which one you think is cute or even what element (grass, fire, or water) you like best and get that type. Hope this helps.

i can answer that!
mudkip is the best
treeko is the worst
and torchic is the mid.

You should just chose wich one you want. It's more what type you like, than what type others like. For example, i started with charmander in red, cindiquill in silver, and torchick in ruby. I guess I have a thing for fire starters. But it's all up to you. Don't let anyone try to tell you what do start with. Got it?

It doesn't matter which one's you start with, you just have to be strong.