Based on results the last few years, Vasek is the number 2. Frank never pulled off a weekend like Vasek did in Israel, and look at his choke in Mexico a couple years back. However, the problem is that all of our potential number two's are so far off world class level we'll have to wait unfortunately for Peliwo to realize his potential in order to match the big guns.
I know, just saying if Vasek isn't ready.
Frank can win too, he beat Nalbandian, Delpo(granted before he was that good), he took a set off Rafa, beat Roddick(retirement but wasn't Frank up a set?), Kohlschreiber, he hasn't done it in Davis cup, and he doesn't do it often, but once every blue moon he can pull a nice upset