If you want advice, use the Help thread sticky please at the top of this section. To be honest most Pokemon in the game will prove useful as long as you train them enough - just go with what appeal to you from the 2nd Gen Pokemon - Mareep line is nice and early, any of the starters are good too and provided you have a Pokewalker/Use the Safari Zone with some as well you can exploit the likes of Houndour/Murkrow(Hoothoot is another flying type early, Togepi line is also decent after some trading + evolution)/Heracross/Larvitar/Swinub/etc are all fine Pokemon when fully evolved for instance.
And if you want a in-game team rate there's a subsection for that too, but you need to include the planned/current team in the thread's opening post I believe for that section. (There's another section for competitive). At any rate, closed.