i can take him.
Tau. Because I'm a long ranged kind of guy
Squiggoth. I think it's better than all the other units because it can do CC as well as ranged combat, and it absolutely pwns.
Necron Lord. All those lovely effects!
Best Race: Space Marines, the Marine squads have a variety of upgrades good at cc and range very good variety of vehicles healer units, deep strike even a hole army of scouts with probes and snipers can kill anything(except daemons and vehicles of course).
Best Elite: Grey Knights, they are available very early in game and with a chaplain attached they rape anything.
Best Relic Unit: Avatar, simply because it's a cc unit and the other Eldar units near him are immune to morale.
Best Commander: Necron Lord simply because he has a variety of skills and can transform to the Nightbringer who is Immortal.
Best unit: Baneblade (seriously, the thing has, like, six turrets. It pwns.)
Best race: Space marines. I prefer to play as chaos marines because they have better infantry, but the SM's Hellfire Dreadnoughts kick ass.
Best commander: The chaos lord (especially once you get the Demon Prince upgrade or whatever it is called)...