I've used dozens of different brands of speakers in my career and I do like a few better than others.  But, this article deals more with types and sizes of speakers, not with the brand choices.

The main mixing and mastering speakers I currently use are Dynaudio 100w powered studio monitors with 7" woofers and 1.1" tweeters.  They have nice EQ adjustment options on the back and I know these speakers very well.  If you get speakers that are a little bigger, you'll get better LOW-end out of them, but I'm happy with the size I use.

The most important part of your speaker setup (that a lot of newbies don't know about) is having a sub-woofer on the floor between your main studio monitors. It's impossible to correctly mix or master any music content under 150hz without having a sub-woofer.  7-8" studio monitors will not play the low 50hz sub-bass AT ALL, and they're weak at best in the 100hz area.