Just came back from several A320 flights down to SFO/LAX, the best seat in the whole Y section is row 12 because it's the bulkhead and there's that empty slot on the bottom of the divider for J & Y where you can really stretch out, however, there's also a chance that you might get a (screaming) kid beside you. The second best is row 13 or 14, it's the exit row so it seems to have slightly more legroom than other rows.

I am not sure whether AC will open up the exit row for you if you don't have any status. Last couple times they assigned me that row when I made the booking.

I try to avoid the back of the A320 if possible because it makes me feel very cramped.

Hope this helps...