I used to ride 53/39, but I have made a switch recently to 52/36. There are mainly two reasons.
1) Versatility - When racing, we usually use just a big ring unless there some steep and long hills included. But when going to Italy to tackle big climbs tsometimes the 39 could a touch too much.
2) Narrower cassette - I hate jumps in shifting so I prefer 11-25 most of the time. And with 52/36 it works perfectly. You have climbing gears and also narrow cassette for flats.
I agree with this. I recently moved and because of a change in terrain went from 53/39 to 52/36. I love it. Where I live now, it's either flat or short/sharp climbs. By running an 11-25 I have everything covered, and the switch from 39 to 36 is essentially one cog in the back. IOW, the 25 now is the same as if I had a 27 before.
If I relocate to an area with different terrain, such as where I came from, I'd simply replace the 36 with a 38. I think 52/38 might be ideal for most locale.