I'm not exactly a sucker for low-middle gain and that's what I found the F-50 to do best. When I play through a Rectoverb, it's a completely different experience. Much fatter distortion and much more useable in my taste.
The one thing that really pisses me off is when people label them before they give them a fair shot. You'd be surprised at how versatile it really is. Just because it can hit the high gain mark on the spot, doesn't mean it can't do the others. I'm constantly pleasured at how you can roll off the gain and presence and get extremely sweet tones for a more classical drift.
My choice: Rectoverb.