I think with modern compacts and derailleurs, you should be able to use virtually all the gear combinations. I seldom find myself using the small/small (34/12) combination, but commonly use the large/large (50/27) at least for brief periods - e.g., going up a significant but not outrageous hill in the big ring, and slowly moving up the cassette, if I find the 50/23, then 50/25 combinations too much, I'll just go for the 50/27 for a while. If it were a longer haul, I'd switch to the small ring.