Whatever you happen to need for your current use.
Do you need something that reaches far? High candela is what you want, and usually getting that range means you need either decent output (lumens) or a large reflector (which means a VERY narrow beam, higher lumens allow for the same range with a wider beam).
Do you want something very floody to light up a wide area? Then you won’t really care about candela/intensity.
Candela per lumen is one of the most useful stats for getting an idea what a light’s beam is like.