As some thers have said, it all depends on which coaster it is. I prefer the front on Diamondback, Firehawk, and Flight of Fear. I prefer the back on The Beast and Adventure Express. Either the front or the back is fine with me on Flight Deck. As for some of my favorite steel coasters, Maverick in the very back seat is awe-inspiring to me, the only ride I got on Dominator (My favorite steel coaster.) was in the back row and I LOVED it, Millie is great for positive Gs in the front, and Dragster's launch is great when you're towards the back. As for my favorite wooden coasters, The Voyage is good in any seat really, but I do slightly prefer the back, Thunderhead gave some great air in the front, but not the back for some reason (Can someone please explain this if you know why?), and I prefer The Legend slightly more towards the back. The only coaster I really have a preference with which side I ride on is The Legend. I'm a big fan of lateral forces, and I feel the lats more on that side than I do the right side.
As for Vortex, I tend not to ride it these days, but the best ride I got on it last season was in 4-1.