At the time I visited, the quetzal was on the Volcan side, however, the guide at Finca Lerida claimed that I visited them at the most difficult time to find the bird, and that summer would be much easier. Just a less rainy and windy period would have been much better
Based on the excellent birds we did see in the volcan area, that might have a small preference in my mind; however, there were other birds we would have missed. If you are going to try for Timberline Wren, Volcano Junco, and probably Sooty Thrush, then you probably do need to do the Volcan Baru Summit road (which probably will take hiring a guide with special vehicle unless you want to walk up something like 13.5 km and 1600 m elevation change); that expedition starts from the Boquete side. I remember reading a report saying that the Quetsals were easy up there in late spring.
So I am sorry, I really don't want to make that decision for you
Niels