I like the metal caps, only 'cause they are gasketed, and if you have a valve issue on the beach, you can usually get a tight enuf closure with the cap at low pressure to get you off the sand.. even tho I carry a valve tool and extra valves, I like the added insurance of the metal caps with the gasket.. I just wish I could get the plain jane ones I usta buy, now they are all shiny, chrome or SS.. bright stuff on a beach ride, don't stay that way... little (very little) naval jelly on the threads keep them from getting permantly attach too..
I always keep an extr set in the glove box, just in case some kid likes the shiny bright ones.. take comfort in the fact that the puke that took them will have them stolen in turn by another puke, and so on, and so on...