The answers are
Is this compatible with Open Cities Reborn?
a) No, not really, though some of the cities and other features are identical. I'll let Samson go into the details, in case I get something wrong and make a fool of myself
If not, which is the better one to use?
Personally, I prefer OCR because all the new layouts and content are much cooler (I still would like a few more new houses in some of the cities though). Further more, the mod is no more problematic in terms of compatibility or the likes. However, if you prefer the vanilla city layouts, then use Open Cities Classic instead.