Having taken one-on-one lessons, and having taught in a group, I will say that you get a lot more out of the individual lessons. However, group lessons can work, too. The key to any attempt to learn an instrument is that you get out of it what you put into it. It's not enough to practice an hour a week. When you first start, it's 10-20 minutes a day (gotta build those callouses). Once your fingers get toughened up, it's 20-30 minutes a day. Then more. The key is playing every day.
I also can not emphasize enough the need to have a good, playable, steel string guitar with good strings and a good set-up. I've had people bring in "Dad's old guitar" that was hard for ME to play, and then they would complain that learning to play was "too hard." A bad guitar is a bad guitar. And I'm not a big fan of trying to learn steel string guitar on a classical. Tough to do.