I've only hear Ratatat and Crystal Castles. Or is it Crystal Antlers I heard? Maybe Crystal Stilts?
Whatever, regardless, it's always good to get out and support anyone you're interested in when they come to town, but If you could only choose two, I'd choose those two only because they're the only ones I heard.
I always try and buy some merch but usually by the end of the night I've spent all my money on booze.
I bought an awesome Fucked Up cassette a couple weeks ago. It was all I had enough money for.