You're talking monitors here? That's what the comment about "per stage monitor" makes me think anyway...I have little experience with anything but mostly Peavey monitors, I like the 15's with no horns best, the horns tend to increase feedback possibilities. Any good brand should work, as long as the impedance is right for the amp.
I'm also looking into the close range monitors, small and a couple of feet from your ear on a stand, and from what I've been told they work great and it's almost impossible to get feedback because they are usually pointed away from the mic instead of sitting under the mic pointed at it. Many also have their own volume control so you can easily adjust to your liking once you get a ballpark setting on the amp. Again impedance is your main consideration, and make sure they can handle the wattage of course.
If you're talking PA, then again I've dealt with mostly Peavey, Spx series usually, they are hard to beat but you'll need a fork lift or a couple of friends with good backs who like a free beer or two...Some of the newer Peavey wedge shaped mains are very good sounding, and not as heavy, but don't get the acrylic boxes, they don't sound near as good as wood boxes. (not enough bass, too much midrange from what I've heard) Some of the Yamaha mains do pretty well, but I've only used them in one band myself, 10 years ago. They sounded very good though and we pushed them with a 400 watt Peavey mixer. Everything I've seen by Behringer looks and feels so much like plastic I quit even looking, I wouldn't trust anything they make going by the quality of their mixers...or lack of it. Nady...maybe, I haven't used any or heard them in use, but the main difference is going to be the box if the speakers inside are good ones. That's the main thing to check, if you see Emminence or EV the speakers should be good, then just check out the quality of the box, power handling and impedance. Some other speakers are good too, those are just the first two PA brands that come to mind other than Peavey's Black Widows. Kustom is back in the game, if their speakers are anywhere near the quality they made in the 60's rolled and pleated era, I'd definitely take a look. I'm running a '67 2x12 cab with my Peavey MX, loaded with 2 Emminence 12s, I love it. Cheryl Crow's band was using all r&p Kustom cabs on the Soundstage video I saw a while back, nothing else on stage at all. I'm not sure if that included PA mains, I'd have to dig it out and check but I think they were. EV is another one to look at, they've always made good stuff.
I'd go with 15s if possible, not for volume level but bass response, both should handle the same volume level. 12s will work, especially if you're only going to be running vocals, but if you mic a whole band or mic a bass drum the 15s will do a much better job.