I usually check them out at the library and then decide if I might want to get a subscription. I also browse through them at JoAnns or grocery store and occasionally buy a copy that looks like it has patterns I'll like. To me each magazine appeals to a slightly different style and kind of quilt(er). All the quilt magazines let you order a free copy to try, that would also be a good way to figure it out.
Currently I'm liking American Patchwork and Quilting. I've only been quilting about 2 years and I like fast and easy. Almost every project in the new August issue appealed to me!