I would use a pair of
entry level B&W speakers (such
as 602's, 705's, CM2's, etc.) before I'd use almost anything that says "studio monitor" on it. Not just for mastering (where "studio monitor" isn't even a word), but for tracking and mixing, give me nice sounding, full-range "HiFi" loudspeakers any time.
"Studio Monitor" is little more than a buzzword fluffed up in the last 15 years or so... Studio monitors used to be massive (no pun), overbearing, anything-but-flat-sounding boxes in the mid to far field that were wonderful to use. They were giant "HiFi" loudspeakers for the most part. Now (with some exceptions, usually based on HiFi designs) it means small, sterile, anemic little boxes that only sound decent from a yard away. They're made to take the room out of the room - A compromise. Of course you had to familiarize yourself with "real" loudspeakers - That's part of the process. But the same goes with "studio monitors" anyway. Most of them carry *essentially* similar specs, but none of them sound the same. If they did, there would only be three to choose from.
Larger Genelec, ADAM, Dynaudio - Good stuff. *Still* not remotely similar sounding speakers either. But for almost anything that you can get at GC, MF, SA, etc., put them up next to a pair of 705's (or maybe 604's if you're looking for something "bigger" sounding)... You'll wonder how you ever got by.