Since OP was looking for the relative merits of a 228i ragtop vs the M235i ragtop, and having owned a 2015 228xi ragtop before it was recalled and crushed by BMW and now having had my new M235xi ragtop replacement for over 7 months, I'll throw in my 2 cents into the conversation.
My opinion of the difference between my 228i ragtop and my 235i ragtop has not changed since I posted my comment on the subject back in March 2016 (url below).
http://www.2addicts.com/forums/showt...3#post19518853