Remember that C+ only gets you extra legroom and better drinks and snacks. Seat width (and thus proximity to your neighbors) is the same as regular coach. Regardless of regular coach or C+ my coach-class seat preference is always like this:
1st choice: Aisle
2nd choice: Window
3rd choice: Book a different flight if duration is longer than an hour.
I'm 6'2" tall with fairly broad shoulders. There's no way I can sit in a middle seat without rubbing shoulders with my seatmates on either side. If one of them is another guy like me we're extra tight. With POS I get the full lateral body experience.
I'm GM now and was PM for 7 years before that, all domestic flights. So far I've managed to avoid the dreaded middle seat, except for the short 45 minute flight between DL hub and my regional airport.
It's hard to make a suggestion for the OP though, since he/she seems open to sitting in a middle seat. I'd need more info first, like flight duration and body size. Big guys like me love to see petite or "compact" people in the middle seats.