My favorites...

Blackburn Multi Mirror. Pros: Stays in place really well once it is set, highly adjustable for different views and positions, large viewing area. Cons: Sticks out pretty far - fine for flat bars, but I don't like it on drop bar applications. Other Features: I once disassembled one of these and bolted it directly to my handlebars rather than dealing with the plug.

Third Eye Bar End Mirror. Pros: Good viewing area with a small profile, stays in place while riding. Cons: Bar end installation can be a bit more fussy; will move around if you e.g. bang your bike into something or crash.

I don't like helmet or eyeglass mirrors - never have, never will. YMMV.