Welcome to FT!

First, I think you might get more/better answers in the miles buzz forum.

That said, I would base my choice on what airline served my area best. Most survey sites etc. participate with a number of different carriers. For instance, erewards can transfer to Delta, Continental, American, NorthWest, US Air, and Air France/KLM.

To get miles from all of the different types of sites, you might have to get two different accounts, since no site works with all airlines.

Good Luck!