I've heard that Vista's issues were fixed by the first service pack. All of my experience with Vista was pre-SP1 and it always ran really slow, which apparently had something to do with Vista's Aero graphics hogging memory or something. Seemed buggy overall.
Windows 95 was a mystery since I didn't know much about computers when I used it, Windows 98 was great for the little PC games that I had access to at the time and was very practical from what I remember, Windows XP was pretty great and most of my computer-learning occurred during my time with it (including learning how to deal with viruses, which is a skill that now earns me roughly $20 a month from friends and family asking me to fix their shit), and Windows 7 feels like a natural follow-up to XP that carries over most if not all of the good qualities.
Windows 8 seems to be built for use with tablets and touchscreens, which seems weird and gimmicky. The design seems like they tried to make it easier for non-tech-savvy people to use, which annoys me and seems to get in the way whenever I try to accomplish something that they don't have a button for. It almost feels more like a smartphone OS than a computer OS to me, and I wouldn't use it instead of 7.