I have limited experience fishing in waders, has only done it once when MJL lended me his old neoprene one for the trout opener this year. However, I can say for sure that when i'm to get one, i will be looking for breathable for sure.
We fished from 5am-12pm, walked up and down the river and the water was quite cold still. At the end of the day, my pants which I wore inside the wader, is completely soaked ... from my own sweat. It was pretty disgusting.
Besides it took a while to put on/take off. Although it's not THAT bad, the breathable ones MJL was using sure looked much easier to deal with.