I prefer shrooms to acid, but I still do both. Generally speaking one blotter of cid is substantially more powerful than a gram of shrooms. Each can be unpredictable and since I've had some bad trips this is of concern to me. A bad trip on shrooms is far more do-able than one on acid.
Now, at the risk of sounding like a granola kid shrooms are just divine if your out and about enjoying nature. Acid doesn't seem to have this special relationship with nature and is best done indoors in my opinion. Shrooms are okay indoors, but I didn't care for it much when I've done them at a night club.
As far as visuals do acid is more potent and produces more exploding colors in my opinion. While you'll get some of this on shrooms, I find the visuals to be well... it's like your seeing the world as it really is, but your mind is so clouded you never see it as it really is. And, how it really looks is beutiful. Okay, I'm rambling silly trip tales here. Try em both. If I could do only one though it would be shrooms.