Spectrum's for me - but then again I haven't tried the very latest TwinHam's that are
supposed to support dual cards. However, even with a single card un-installed in device manager, the TH 1.2 drivers resulted in a hard lock up when scanning channels pretty much every time.
Spectrum's 1.6.0 supported dual cards nicely, and his patched 1.6.0's actually seemed to work a little better in a single card PC. What's more, his 1.6.0 drivers scan way faster than TH in a single card machine - and way way faster in a dual card machine - since the TH drivers locked up every time!