What horns are you looking at?
If your at all interested in horn speakers, I would advise that you try to listen to as many different design as you can. Just to see if you like them or not. The upcoming (Oct 8,9,10)
Rocky Mountain Audio Fest. I'm not entirely sure who'll have their speakers at the show...but it should end up being pretty darn good.
Horns can certainly do some things very well. Such as dynamic range, micro/macro dynamics, ability to play well at both low and high volumes while maintaining good control over the music at all levels. They can really sound quite good!
Some areas where horns can have some trouble are with tonal accuracy, beaming and listener fatigue (to name a few). Horns can actually sound quite bad.
There are certainly horn combo's out there that I haven't heard...but my favorite horn/driver combo is for a EdgarHorn "saladBowl" with JBL drivers (1" or 2"). To me, this horn combo has good tonal accuracy while maintaining the other aspects that I like about horns. I've also heard the same JBL drivers with other horns...to my tastes...they weren't as good.
Another driver combo I like are the classic altec compression drivers. Even tho I've heard the Altec drivers also on EdgarHorns, I preferred the Altecs on (slightly modified) Altec horns. To me the Altecs will always sound just like Altecs

They got that BIG Altec sound...gotta love it
I've heard a few other compression drivers/horn combo's...but the two above are my favorites. If you get a chance to audition some horn speakers...don't rule them out entirely just from one or two auditions.
Also note where the speakers are crossed over at and to what. The better horn systems I've heard are full blown horn systems. While you can make some compromises (as I did), you still need to be careful with speaker selection for the midbass woofer. Most times sticking with a higher efficiency lower distortion midbass woofer can get you decent results in a sealed or vented cabinet.
Some other horn "type" systems I've had a chance to listen to are the front loaded cone type horns. Like AdvantGarde duos and Oris Horns. Both are quite nice in their own way. The Duos I heard were some of the older versions...and I've heard they've cleaned up some wrinkles in their woofer...but when I heard them the bass was having some troubles matching up with the horns. But the horns really have a neat sound to them...the presentation was/is unreal. I could only imagine of you would hook up a nice 845SET amp to these things you would be transported off in some dimension yet unknown
Last (finally, huh

) My favorite Lowther/Fostex type rear loaded speaker would be the new version Lowther pm2a's in Medallion enclosures. I've heard some other versions of rear loaded speakers that I thought ranged from very nice to pretty poor.
Again, it's best if you can get out and judge for yourself. While I do like several different horn type speakers. If I could only recommend you only listen to one horn speaker, I would recommend that you listen to the EdgarHorn TiTan system. Not because I think it's the best...or because I think there aren't any better speakers out there...don't be concerned with what I think of them. But I say this because I know that speaker fairly well...and it has several of the qualities that make up a good sounding horn system.
take care!