>>8333158After buying a few figures from each line...
McFarlane is unquestionably more "quality" looking. More paint detail, more detailed sculpts. I also find them very easy to pose, with a nice range of motion. They are a weird size though, a little too tall to be 1/12, and the character choice is currently pretty limited.
Jazwares is more "fun" looking, with bright poppy colors and lots of accessories. Some of them come with a few swappable faces, which is a really nice touch. They have more joints on paper, but they ratchet really hard and range of motion is kind of limited. I don't find them that pleasant to pose. The hinged fingers are kind of a pain, but not as much as I was expecting. I still wish they would have put a peg in the palm to hold things more securely. They are close to Marvel Legends size and fit in really well with most 1/12 figures.
Both lines have their ups and downs, really. Maybe try one of the cheaper ones from each line and see how you like them personally.