I'm going 50/50 with BTC/LTC right now (for every 1 BTC I mine, I buy 1 BTC worth of Litecoins).
At the current difficulties, and given the viability for GPU mining of LTC, you would do better to do that the other way 'round - Mine LTC, and for every 800 or so LTC, buy one BTC. You'll have a few LTC left over, and still get a 15-20% better
BTC yield overall.
This is no longer true for me after the difficulty change, but that doesn't stop my from mining though.