Some of the most successful implementations of a point source I've heard (which is what coaxial comes down to, being a point source - certainly over a relatively wide frequency span, if not most of it) is the Synergy horn by Tom Danley and TAD's CR1, but I'm also quite fond of the WLM Diva's (10" Eminence coaxial). I've found the Tannoy Dual Concentric iterations a bit too "flavored" or heavy/dark sounding to my ears, albeit with a very easy-going presentation and distinct sense of a coherent "radiation bubble" in front of me - a vital trait to aspire to.
What I'd consider the most here is a Synergy horn, but even being large I find they tend to lack a wee bit of upper bass energy that can be more successfully achieved from a dedicated midbass horn. So, instead of going with a 2 or 3-way Synergy horn crossing over to a midbass horn at 3-400Hz and then subs ditto further low I'd rather skip the Synergy horn altogether and go with a larger format MF/HF single-driver horn that takes over from the midbass horn on up. Being careful with timing/delay and maintaining uniform dispersion patterns at the cross-over frequencies a very coherent radiation sphere-of-sound can be achieved, while having more dedicated driver/horn sections to their respective areas. More of a hassle for sure, but to me at least ultimately more rewarding.