I like both bands a lot, and have all of their albums (well, Heep through Abominog that is). It's hard to pick one over the other, because each has had unique and important contributions. The Heep had a more overtly progressive beginning, but BOC has had more consistent - in my opinion - control over their music. I appreciate the Brit influence of the Heep, but also the American twist in the BOC. The Cult had some great lyrics and imagery from Sandy Pearlman, a respectable writer and observer of time and history in his own right (but that's cheating a bit, since he wasn't specifically in the band).
Just enjoy both! We have two hands, so why not fill two goblets with your favorite wine, mead, or beer, and give two hearty toasts! We don't need to poison prog by descending to western ways, and getting competitive, etc. An eastern approach would be to value both; addition rather than subtraction (1+1 rather than 2-1). One way rises up, the other goes down...
Edited by Boojieboy - September 27 2017 at 10:03