I've used both, but really liked the standard size. The standard size has a larger field of view, hence I did'nt have to re-adjust it when I was wearing a jacket that might bunch up a bit on my shoulders. I lost that one on tour, and happened to have a compact model as a spare. The compact has a bit smaller field of view, and I have to adjust it a bit if wearing a jacket.

The compact is still pretty decent, I haven't gotten around to replacing it (with another standard sized) yet.

Tip for folks who get a "take a look". Put a bit of tape on the back of the mirror to keep the mirror from scratching off. I use some spare 3m reflective tape, but even scotch tape would work.