I'm still trying to figure out what all makes a speaker sound good to me. I can learn to like a lot of speakers, but I have found that when it comes to direct radiators I tend to like a 4" cone midrange, and 3/4" dome tweeter on a minimum baffle. Crossover up around 3500 Hz. Small bookshelves like this tend to have a great effect on me, often better than 2 ways with larger woofers, even though I can hear improved bass extension and lower distortion. Just add woofers/ subs to the little speaker and it's great! It's something about the dispersion characteristics of the smaller woofer and tweeter I suppose.
For horns, I like full horn loading rather than hybrid designs, and smooth dispersion characteristics rather than full exponential loading like a Klipschorn of old. I think some degree of smooth off axis is taken into consideration on most modern horns now days.
In any case, I'm willing to try anything. If it works, it works. But if I were forced to buy without hearing I'd be looking for smooth on and off axis response with high efficiency and relatively easy impedance load. I'd be willing to sacrifice maybe some smoothness in response for better efficiency, so long as it's not too rough. I'm willing to sacrifice absolute impact / loudness for a smooth, natural and detailed sound. I don't like it really loud but I've experienced a sound I prefer more often with higher efficiency speakers.