I tried a glasses mount mirror and couldn't get used to having it in the corner of my eye (must be me; I also turn off the compass in the mirror of my car!).
I have tried myriad bar end mirrors.
The Italian ones are too small for my old eyes, aside from the fact that you have to get them lined up just right when you wrap the bars.
I liked the Sprintech and Zefel Cyclops mirrors, but found that the mounts break.
I have come back to the Mirrycle; I use the one for flat bars but leave out one section of the mount. It has been very durable, is large enough that I can see what is coming from a useful distance, and can keep track of the people I am riding with on the rare occasions when I am ahead.