Probably the rims (tires, wheel hub fit, balance).
You could swap out for other wheels (old ones) to see if that's the problem.

Things to check:
Balance
Hub fit-are the new wheels hubcentric?
Crap between the wheel and brake rotor
Loose suspension parts (wheel bearing, tie rods, ball joints)
Brake rotors warped (especially if they thump when brakes applied)