I've had and seen both..hands down led..if money not a option..with led.you have to damn near cover to entire canopy with lights.
I'd vote led if there was a capable diode functioning in the 290-320nm range. If money wasn't an issue, I'd have me a few of those Spectrum King SK602's, seems they are releasing a new version sometime this year.

Love my 315 rigs though, the Philips Elite Agro 3100k are magical little bulbs, and see Grower's Choice just put out a 500w single ended cmh rig I wouldn't mind taking for a spin.