As I mentioned in another thread, I've only really been to theme parks here in SoCal (ie., Knott's, Disneyland, and SFMM).
The only GCI coaster I've ridden is Apocalypse at SFMM, so technically it's both the best and worst GCI coaster I've ridden. I wouldn't wait in a 2-hour line for it, but I do love that ride. I suppose you could count Ghostrider at Knott's as a GCI coaster, since GCI refurbished it last year, but I haven't ridden it in at least 5 years.
SFMM and Knott's have their share of B&M coasters, and I have to say my least favorite is Riddler's Revenge. People complain about Viper being rough, but I can ride it 3 times in a row before getting a headache (which I usually do, because nobody ever goes on Viper ). But one ride on Riddler's Revenge gives me a headache AND leg cramps, every time.
As many times as I've been to SFMM, I've never ridden their Intamin coasters, so I don't have an opinion on those. I've heard Green Lantern is painful, and Superman is closed every other time I'm there. Flashback was long gone before I started going to MM.