After fighting issues with NextGen and some of the others, this one worked first time, every time, and editors have no problems figuring out how to use it. It's light on the server and fast on delivery. I found one three column theme I'm using where I had to go in and tweak the layout, but, other than that one theme, every other blog theme was fine. This one is the best, especially if you want easy, fast, and "it works" as your top qualities for a plugin.
No issues at all when upgrading.
:D