Electric fans are a great way to get a couple of extra HP. The problem is that they just don't do as well a stock fan. Used in conjuntion with a stock radiator and most of the time your asking for problems, But it really depends on the size of the radiator. If you have cooling issues now, don't consider an electric fan.
I started with a black magic fan on a stock 3 core and ran into problems fast. It wasn't the fan, the radiator was too small. The stock fan was overcompensating for the poor radiator.
I now have a Griffin alum radiator and 2 Mr.Gasket fans for a total of 3200cfms.
The cooling area is one place that BIGGER is always better.
If you only want to use one fan, look for the biggest fan that will fit your application. Spal fans seem to be the best from the aftermarket, but they are expensive.
I liked the Black Magic that I had but, with the Griffin radiator it no longer fit. It was worth the money. It has a thermostat and a shroud built right it.