Front, usually the smoothest, gives the best views, most times gives more airtime and I just prefer it to any other seat. Examples, Megafobia is very good at the front, smooth with some amount of airtime, but in other rows it's very painful and airtimeless. Also EGF back row gives a lot of vibrations which spoilt it a bit, but still gave epic amounts of airtime (less than the front still)
Back rows for me are just for first drops like on EGF, Katun, PMBO and for the helix on Nemesis. They are also a lot of the time, exceedingly painful a la Colossucks etc.
So front, but I tend to try to sit in most seats before finding my favourite seat.