I guess it depends on the board and waves that you are surfing. Over the years I have collected about 20 sets of fins so I am my own test drive centre

On a 6,3 square tail I would normally go for PC5s on my quad I hace Sunny Garcia side fins with GX-Q rear fins, best combo so far.
On my 6,8 I generally use DHD2 fins but if I have to use it in small waves I will use a PC3 just to loosen it up a bit.
I find that glass fins are so much better than plastic fins, they generally have more drive and make the board feel more responsive.
Its all about feel so what ever feels right for you.
Feel free to PM me if you have anymore questions