Remake is for people who loved the Midgar parts of FF7, Rebirth is for people who loved the non-Midgar parts.
I knew a lot of people who didn't like Midgar, but I was always a Midgar guy. I wish Remake had expanded on it more. I think Chapter 3 was the only part that actually showed us more of Midgar than what the original game did. I wanted to walk the streets of the upper level and whatnot, not just hang out in the (way too bright) slums for 30 hours.
Rebirth is a much better game than Remake, putting all that other stuff aside. 90% of it was fantastic, though the handling of Dyne midway through and Aerith at the end were both completely retarded and sanitized as fuck.