I have been making cakes for many years and they have rarely ever
stuck. The procedure is as above, greasing and flouring the pans. I
really don't think it makes a difference if you use butter or oil or
Pam. I usually use butter if there is butter in the cake, and oil if
its an oil based cake as many bundt pans are. Cool the cake and turn
over on a rack for a while. Sometimes its helpful to stick a knife
around the edges between the cake and the pan.

I think a big difference is using a non stick pan. I have an ancient
bundt pan that is very heavy and it can be hard to get the cake out of
the pan. I recently bought a new non stick nordic ware bundt (they had
them at TJ maxx) and I sprayed it with Pam and the cake slid right out.