I agree that in a room your size, a good pair of monitors is the way to go. I don't agree though that a good pair of floorstanders cannot be purchased for $1500 brand new. I can name many good ones that use quality drivers and pay attention to cabinet design to reduce resonance at this price point. Whatever construction and components are use, they still have to sound good to you and be the best the speaker for you - not us. So asking a bunch a strangers in a forum for a recommendation is really pointless. Instead ask yourself these questions.
1. Whats amplification do I have or plan on getting? Does it have a large enough power supply (not watts per channel) to drive low impedence speakers of 4 ohms or less? Should I even be looking at low impedence speakers with sensitivity ratings in the low to mid 80's or should I stick with 8 ohm, more efficient speakers witrh ratings in the 90's?
2. Whats my room like besides its size? Are there a lot of hard, reflective surfaces? Window? Hardwood floors or carpeting? Or is there a lot of plush soft furnture and drapes that can absorb sound.
3. What kind of speakers, particularly tweeters, do I like the sound of now? What have I heard that has already impressed my ears? Do I have a baseline for listening? Tweeters come in all differenet types - soft domes made from different fabrics, hard domes made from different metals, ribbons, ring radiators and compression horns. All these types sound different from one another. At the same time, they can all be good. So the trick is finding out what sounds good to you.
I would start asking myself the above and then go out and start auditiong speakers by type (not brand) to narrow down your driver preference. Also bring along source material that you are very familar with. One you have made a short list of actual models you have heard, then come back and ask forum owners about the specific models you are thinking about. Most will be glad to tell you what they like or dislike about them. Good luck in your search.