I think cassette choices are entirely personal and depends on the rider needs and strengths. Currently have compact crank with 12-27 (came with the bike) but for me, this is completely unnecessary. I really liked the compact crank, but the jump between 19 - 21 - 24 - 27 is so drastic that I cannot seem to get comfortable with my cadence. I am currently in a shopping mode for 12-23 or 12-25, since I rarely use 27. But if you have compact crank, assuming that you are not going to be climbing an epic mountain, 12 - 23 might be an OK choice.