Gaeren said: Aluminum with a plastic liner that can be changed works well.
We use the aluminum with the plastic insert. We get about two years out of the cups and change the liners every few months. The liners are like $1 a piece, so it's no big deal to change them when needed.
The plastic ones wear too quickly in the wind, and will break when a golfer slams the stick in the hole. The upside is they are much cheaper, so you can change them out more often.