I'm a big fan of Jensen copper foils. I've tried Orange Drops, Kommie Kaps (K40Y-9), Solen, and Clarity Caps in my GSG, and the Jensens have a very "flesh and blood" sound to them. Second favorite were the Kommie's, they sound pretty close to the Jensens but lack much of the midrange bloom that is prevalent with the Jensens. Third would have to be the Orange Drops, very nice for the money and a good all around sound. I didn't care much for the Solens or Clarity Caps.
EDIT: I'd like to add, these were my findings in the particular amp I'm running. The circuit of your amp may like something else. Best thing to do is buy up a few different kinds and experiment. One doesn't need to spend large amounts of money experimenting with caps, as there are many budget-friendly offerings out there that you may like. Orange Drops, K40Y-9's, Solens, and the cheaper Mundorf offerings are a good starting point for not a lot of cash outlay.