I'm more comfortable on a zero setback post, but I think it's mainly because I have very short legs - 5'10", and 30" inseam pants (the shortest you can typically find off the rack) often drag. As such, a setback post puts my knee too far behind the pedal... I think. I've never been able to get into a comfortable spinning cadence with a setback post, but can with a straight.

Also, for future reference, if you have a 31.6mm seat tube, you don't necessarily need a 31.6mm post - there are adapter shims that will adapt a common 27.2mm post to 31.6, which opens up options a bit. Current trends are to have a skinnier post that'll have more 'give' over bumps; 31.6mm seatposts are used for more frame stiffness under power.

As someone above mentioned, two bolt posts are great - I've sheared the bolt off of a single bolt post in the past. My preferred option is a Thomson - my Elite is 22 yrs old (replaced the single bolt that sheared), and is now on its second bike.