Keep an eye on www.coinwarz.com and www.dustcoin.com to compare the relative mining profitability of each.  At this very moment they're fairly similar so it's probably easier to just mine Bitcoin.. But if the Litecoin value rises in proportion to Bitcoin, or Bitcoin difficulty increases quickly (which is supposedly likely in the near future) then Litecoins might be the way to go for GPU miners.  But the charts on those sites should reflect that if it comes to pass.