So, I happen to have both and will offer the following observations.
The big thing is the quite obvious ergonomic and size difference. Roof vs, porro-night vs day. Sometimes I like one, sometimes the other. I would not say one is better than the other, just that they are different. If I was put in the position to choose one, I'd take the ZEN 7x36. Why, because overall I think the optics are a little better, and at least for me the depth of focus is better in the ZEN. The focus wheel movement in the Raven is stiffer and stickier than it is in the ZEN.
Tero is right in that the 7x ZEN seems to show a bit bigger image, but that may well be due to the tendency of a porro to show a smaller image than a roof of equal magnification. I can see the difference with the Raven and ZEN, but not with the 6.5x32 Fury and the ZEN.
The Raven will never give up its portability advantage to the ZEN. The ZEN is just about the same size as, say a Nikon Monarch. The centerfield resolution in the Raven is pretty decent, but not quite as good as the ZEN. Neither are stellar edge to edge sharp as some are wont to pursue.
EDIT: Now I see a couple of other posts showed up while I was typing this. Which ZRS do you have? If it is the original, you can solve your dilemma by switching to the new version, which is the most compact 8x42 I know of, and noticeably smaller than the original, as well as the ZEN 7x36. It is very little larger than the Diamondback 7x36 and the optics are better in the new ZRS as well.