[Luv2]

I had an STi ('11) before I traded in on my M235i, but I have driven the M2. The '17 Sti has a nicer interior than mine did. if you did a Stage 1 tune with the Cobb Accessport on the STI, it will be faster than the M2, for about 1K. Subies are super reliable, with a Stage 1 tune.
I see you are in FLA, so you might not need the AWD, I did living in the Toronto area.
The M2 will be smoother and more refined than the STi. I had Subies for about 11 years, but have been impressed with BMW's refinement and handling. I think the M2 will hold it's value more because it is rarer.
Maybe get the M2 and then an older STi sometime. The older STi's are just as fast. Have had the same engine since about '10. Good luck man !