I can't offer a real-world opinion, since I'm not running "proper" protected 18650s and chargers yet. I standardized on AA/AAA NiMHs some years ago and haven't seen a need to change. Have to say, though, that prices on lithiums and chargers seem to have finally come down to earth.

If they're anything like the unprotected Samsung Li-ions I have been charging (very, very carefully) direct from my solar panels, their charge retention should be excellent.

A quick survey of CandlePowerForums suggests that 18650s should retain at least 80% of their charge after a year in storage. If that's correct, it's impressive -- better than LSD NiMHs such as Eneloops.