I'd take the R32.
I'm not a fan of the Civic Si's design. The proportions aren't athletic at all. FWD = Wrong wheel drive. It lacks torque. I HATE the interior (fyi, I used to own an '06 EX Coupe) with its stupid digital readout. The brakes are subpar. It's a Civic. The list can go on.
The R32 at least has some grunt and AWD to boot. Not to mention you can find some tasteful mods for the MkV body style. And the interior is LEAGUES better. The seats aren't even comparable.
Past:'08 E92 335i|ZPP|ZSP|6AT|four (4) HPFPs
Present:'15 Mustang GT|401A|PP|6MT|Recaros
Sig pic unrelated. I like to go sideways and stuff.