I mine the algo that is good for the GPU or ASIC.  If you have a bunch of rigs with the same GPU, then you can spread your hash around, but you need to believe in the coin.  Otherwise, if you are in it for profit, just go with the most profitable coin for that algo.  Unfortunately, that changes quite often, so you need to keep up with it.

There are many schools of thought... pick one and experiment, then pick another and experiment.  Eventually, you will have a sound strategy.