RE: Which performs best, a larger wheel or smaller wheel?
Driller said it very well.
It basically depends on what you want to do.
There are three things in play here, if you neglect tire construction.
One is unsprung mass. The greater the unsprung mass, the harder the suspension has...
oh, damn. rodney dangerfield died today, at age 82. just heard it on the news. What a bummer, he was a good comedian. Too bad, but i guess we all have to go sometime, and he lived a good life.
Anyway. Unsprung mass is the enemy of handling. The suspension has to work harder to deal with it.
Second is rotational inertia. This is primarily important in accelleration and braking.
Third is contact patch. A larger diameter or a greater width will give a larger contact patch. A larger contact patch will give better traction but also greater rolling resistance (usually a negligable factor).
There is no one answer to your question. It's all about optimization for what you want to do. But if you want performance, and you want rims, shop for the lightest wheels you can buy. The term "mag wheels" stems from that. Racing wheels are often made of magnesium because it is very lightweight. However it is not that strong and is somewhat brittle, so it isn't the greatest for street cars.