Test drive all of them.
List features - make sure the machine you're buying has everything you need and at least most of what you want.
Check into accessories - if the machine doesn't already come with all the bits and bobs you'll want, find out how much they're going to cost and if the machine will work with "generic" feet and accessories. (I think Bernina has a special shank so feet aren't as easy to come by - but don't take my word for that.)
Someone might LOVE a machine that is terrible for you! Your own taste/experience/needs/wants are what's going to guide you to the best machine for YOU.
Personally I'm a Janome fan. Their machines make sense to me and everything seems simple and intuitive, and I find them to be extremely reliable. BUT, my very first machine I bought on my own after moving out of my parents house was a very basic Kenmore; I found out after buying my Janome 6600 that my Kenmore was actually made by Janome, so that might be why the newer machines seem so intuitive to me - I've had years of experience with their general design.