Most heros can be decent in a 5v5 if you have a good arrangement of disables (stuns, silences, holds, ect)
in 1v1s, ranged heroes tend to be best, many people prefer nukers, as you can buy a dagon at level 1 (400 dmg)
but once you play the game enough (in 5v5s), you'll realize that the heros that do well solo lane tend to be the best 1v1ers.
as for 2v2. you probably want either stunners or nukers.
anything to kill the other team early on and stay ahead.
a common favorite for many people is Bane elemental, as he can nuke, hold, sleep and harass.
other common 2v2 heros are anyone with good early game skills. this is because in a 2v2, you can buy items to allow you to spam the skills without running out of mana.
edit: as for just learning the game. try to play a hero with at least 1 disable. so that you're learning the proper times to use your skills. many people start out with straight dps heros who have no disables, and never learn the proper times to use them, or realize how important they are for a team.
This post was edited by jstiller30 on May 30 2009 07:15pm