I've owned both. Batman Forever by a mile. Just didn't get into Frank for whatever reason. Seemed like the ball was going in or rolling in the scoops on the left hand side all day long.
BF is very tough and has some really great shots. Some complain about the bat cannon for some reason (slowing down the game) but i love it and I've owned the game for two years. I tend to flip my games after a few months so the fact that i've kept BF for two years says something. Looks great with LED's although I've only put them in the BG and a few specific location in the playfield.
Only negative to BF to me is the lack of audio voice calls. It seems like there is only about 10 calls and they get old quick. I'm not sure why the audio is so limited. Has a video mode and many of the modes as I said are very, very tough. You have to play the game for awhile and/or read the rules sheet to figure it out a bit. Great game IMO !