I've done high doses of both and combined them.
I find mushrooms to have a lot more body feeling in them, you feel a lot heavier and can't walk. Visuals are ridiculously swirly and your emotions change RAPIDLY. Lastly mushrooms are fairly short lived, lasting only about 6 hours from beginning to end with a 4 hour peak.
Acid is a LOT more visual, patterns coming out of patterns coming out of patterns, etc. I've seen amazing shit, things that blatantly weren't there. It is a stimulant so your quite hyper and its difficult to sleep even the day after. The overall effects last MUCH longer, the longer trip ive had was 14 hours, peak lasted about nine.
I find acid to be a lot better, its easier to ingest, lasts longer, you can walk easily, visuals are better.