DEFINITELY The Nightforce.
The ElCan is unreliable at best. The Nightforce is more scope than you'll need for you Tavor or your AR, but you don't want the Elcan. In fact they're both more scope than you need for anything at 50M, I would go with an EoTech/Aimpoint.
If you want something for longer range, get a Leupold Mk4 MRT.
By the way, try a search for the Spectre DR on here, there are already several threads where a number of shooters have listed their complaints with the optic.
Cheers.
Tim




























