Since you have a 3 stream dual band router you want a 3 stream dual band card for best throughout. Like with wired NICs, Intel is one of the best in wireless as well. The Intel Ultimate-N 6300 is their current best which is dual band and supports 3 streams. I haven't seen any desktop Intel wireless cards, so you'll need to look at using a mini-PCIe card in a desktop adapter.
Something like this (no recommendation on the store, just an example):http://www.bplustech.com/adapter/MP2W_6300H.html
If there is little interference in the 2.4 GHz band then use that. In the more likely case that the 2.4 GHz band is crowded then use 5 GHz. It has less range and penetrating power, but can work better if the band is clear of other devices.
If you really care about performance and you have a desktop you should really look at just biting the bullet and running a wire. Even in the absolute best case you will never get even close to the rated speed out of wireless. With a setup similar to yours and an Intel 6300 card I get about 240 mbit/sec real world about 3 feet from the router. Add a floor in between and the speeds drop significantly. Same laptop using the crappy wired realtek gig nic gets about 975 mbit/sec.