Roselia, Bellossom or Sceptile.
treecko it evolve into grovile which evolves into sceptile
Sceptile's leaf blade
Everyone lieks Mudkipz!
The best starter Pokemon in Emerald/Ruby/Sapphire is Torchic. If you level it up well, it'll sail you through the first 3 gyms with ease.
The grass is the best, because in the end, you will need him a lot! It is though only based on preference (But i heard you like Mudkipz)
Treeko(Sceptile) is the WORST!! starter in Emerald, because its weak and only learns 1 good move. Torchic(Blaziken) is very fast and strong and good for fighting the Pokemon league, and Mudkip(Swampert) is sorta slow but really strong. Grovyle is really bad. Sceptile is a little faster than faster Blaziken but so much weaker. Sceptile has low Defense, but the foe can't attack at all if Sceptile KO's the foe with 1 Leaf Blade(his only good move but it wont KO with 1). Treecko, Grovyle, and Sceptile have one type(which makes them even worse!), you can have 5 other Pokemon in your party to cover Sceptile's type-disadvantages. Swampert's and Blaziken's dual-types make them vulnerable to more types(which makes them better). you don't get 2 STAB types for Sceptile as you would for Swampert and Blaziken, you need a second STAB type. Overall I like Mudkip, then Torchic and then Treeko but Treeko is definitely the worst
Torchic, it can learn Sky Uppercut which attacks even Pokemon that used Fly
-Azumarill -Magnetric -Breelom -(A flying pokemon) -(a normal, fighter or psychic)
the best is either mudkip or torchic because of their evolutions mudkip= swampert torchic=blazekin
in my opinion they are rayquaza,ditto,latios,your starter pokemon,aipom and anorith hope i helped
you should train a water Pokemon or teach your treecko rock tomb