When I used to ride road bikes I tried a few different kinds of mirrors. For me personally a helmet mirror was useless! Actually worse than useless since I still tried to find stuff in it and undoubtedly was at least a little bit less safe.

Strong votes for a bar end mirror though. I loved it. I'm on a Surly LHTD now where shifters are on the bar ends. But otherwise that's where my mirror would still be.