depends on your goal.
if strength is your purpose, i would use flat for a couple of reasons. You can use more weight, and it's a competition lift.
if "bodybuilding" is your aim, i would use incline as it supposed to isolate the front upper shelf more than flat bench.(i.e. pecs and front delts.)
also your level of advancement, as said before, should be considered. all this should come secondary to whether you've got a firm grasp of flat bench press technique. (for your goals)
My Training Journal
5' 8" Current BW 207 (94) lbs (kg)
20 JAN 12 at 200 (90) BW
- 385/275/405 (175/125/184) SQ/B/D
29 MAY 12 at 206 (93) BW
- 135/175 (61/79) SN/CJ