On the 737 in CE it's 1F, it has more leg room than 2A. Domestic, on the other hand, always 2A or 2C on a 737. For the rest of the shorthaul fleet I tend to 1F but if 1D is already taken I'll go to 1A and that way 1C will probably kept empty.
On domestics to NCL I always go for 1 C or 1D so I can get away quickly. On EDI I go for 1A down to London, 1F on the way back, continuing a so far fruitless quest to see my farm from the air.