Probably Fleetwood Mac.
Fleetwood Mac was simply THE concert ticket to have in my later-high school and college years, and I still enjoy their rocking, rolling, rollicking music any time I hear it. I considered Heart the best of the soft-rock genre, a type of music I enjoyed for the pleasure and ease of singing, which I also liked to do.
I love music and always could appreciate a lot of different types, particularly in my younger years, though. It makes it hard for me to cite "a" favorite.
Also, my teen years happened to have been dominated by several groups that, musically speaking, were similar, to the point of seeming to be almost interchangeable -- Journey, Styx and REO Speedwagon, Chicago, and Heart come to mind -- and I liked all of them a lot. After that, I was partial to Boys II Men for some time, too.