For a smooth running chain, you want the wheel to be very, very close to parallel with the front chainrings. It's worth getting out a caliper and setting the wheel position by adjusting the dropout bolts. Once that is set, the Park derailleur alignment tool is the best $50ish you can spend for getting clean, crisp shifts.



The Park tool allows you to align the derailleur hanger to be very close to precisely parallel to the wheel and thus the rear cluster. After you've gone to the trouble of getting everything aligned, it's worth having the dropout adjusters to make sure that removing the rear wheel and replacing it doesn't screw up your great shifting rear derailleur.