You'll get lots of different opinions, and your final choice will depends on what you;re shooting and at what sort of ranges.
I've used a Drone Pro, Digex and PARD NV008
I'd rate them (best tow worst)
Drone Pro - great image quality and can handle a wide range of visible and IR light intensity - virtually impossible to white out
PARD NV008 - best day/night option and although it needs a lot of IR, it does produce and excellent NV image
Digex - most sensitive, but whites out very easily, no daylight capability worth speaking about, very "soft" image. Basically designed for shooting large targets (boar) at short ranges in moonlight or with minimal IR. Increasing numbers of people who have bought them are returning them or selling them on because they white out too easily.
PS The somewhat cheaper Yukon Sightline is basically a Digex with the "toys" removed
Cheers
Bruce