yep there are lot of brands out there , but there are only a few thru full turbo manufacturers
HKS , Forced Performance , Precision Turbo , Turbonetics , their majority parts are from Garrett
Apexi are made by IHI
Blitz turbos are made by KKK
Greddy are made by Mitsubishi Heavy Industry
Bullseye main parts are by Borgwarner
KKK , Shwitzer and Borgwarner if not mistaken are under one
there are lot more
many use the GT35 becos its a proven turbo and has variations to suite ur applications in the sense of u want a smallest , smaller , small ,moderate, big , bigger, biggest , monster turbine housing , not all manufacturers have this options
diffrent brand with same specs are hard to find i guess, some are journal, some are ballbearing , diffrent fin design n trims
so it comes back to , whts ur budget, and the power that u want to achieve :D