I like 8" f/6 because it is big enough to show a fair bit, and small enough to get used a lot. However, if you really want to see more 14" f/5 is supposed to be another good point for usability versus light gathering power. I have had some experience with a 16" f/6 (not my own). It certainly shows a sky littered with NCG's, but it's hard enough to use that It rarely gets out. At f/4.5 or even 5 it would be better, but also more specialized.
My personal ambition alternates between a 14.5" f/5 and a 12.5" f/6.
My personal ambition alternates between a 14.5" f/5 and a 12.5" f/6.