I have use 52-42s and 53-39s. The 52-42 is good if your terrain is mostly flat and you ride fast. The transistion from 10T diff w/ the 52-42 is smooth, so I only need to click once or twice on the rear. The 53-39 however is harder to use, since you will have to click twice or more since the resistance change is more sudden.

But, I like the 53-39 better, because I ride hilly routes and I can put 12-23T cassettes and still climb steep hills, likewise my shifting(rear) is smoother w/ my tight cassette. On 53-42, I need to put a 12-27 so I can get low enough gears for climbs.