Question

I like fast, hard hitting pokemon with good movesets.

Answer 1

If you're talking about the event in HG/SS, then you can't choose which one you get. HeartGold gets Latios, SoulSilver gets Latias.

Latios is slightly better with the attack so that's probably the one to go for. But the difference isn't much.

Answer 2

Latios has higher offenses than latias, but only by a few points each. Choose latios if you want that extra bit of power: plus his moves are more attack oriented.

Latias-Tons of helping moves like refresh, safeguard, helping hand, and healing wish. (granted, latios can still learn these as well.)

Latios-Power based attacks like dragon dance, and dragon pulse,

Their movesets are pretty similar though.