Tough call. I would say movement speed as you can easily make up the gold find on other equipment, and movement speed will make your runs faster, probably netting you more gold over the long run.
As a monk I try to always be on the MS cap, something that isn't exactly hard to accomplish with the passive abilities and MS boots. If you can cap MS at 25% through other items and passives I'd go with the 20% GF ring. There's of course also something to be said for getting more DPS.. That in it self could also make your runs quicker.
