As I always maintain: RPM is better. You don't get ripped off, and know the price wherever in the land you may find yourself. It keeps your local dealer alive and brings you convenience as well as someone with a little more muscle than you, and an axe to grind on your behalf.
I know this will be disputed, but they tell me here in Mallorca that the Brits are odd: they will drive the 69 klicks to Palma to save six euros... imagine that being for a lens, and you need to return it three times! Actually, forget that: I never knew a dealer here who would accept anything back unless you were buying something more expensive.
Buy Internet? Only once you know somebody well enough to send your details.