Nothing is sturdier than a ring radiator

@erik_squires --

Just a reminder that the subject of this thread was reliability. :)

As in, exposed to what - time, power, pokey fingers? In these areas regardless nothing beats a compression driver; its diaphragm in concealed inside the whole of its mechanism, they usually take a lot of power (while not least being the most efficient driver type to turn it into actual sound), dissipate heat effectively, and are extremely reliable even after decades of close to abusive use. 

@erik_squires --

I've seen Altec compression drivers blown by 75 watt amps and not overdriven, so not so sure that they are that much sturdier.

That example says close to nothing without any further context. What specific driver are we talking about? Some of the older ones only have a rated power capacity of 15 watts (at ~109dB sensitivity, that is; that's a required 1500 watts for a typical dome tweeter for similar SPL - adios, muchachos), not to mention the SPL delivered at 75 watts on a compression driver of that caliber. As I pointed to already, sturdiness of compression drivers way surpasses that of direct radiators in any form, period. They're easily 20dB's more sensitive alone, real world tested in the pro field constantly, and the sheer output they can produce would obliterate any dome tweeter, ribbon or ESL before they ever got there. Some AMT's (for the pro arena) are high efficiency, so another matter obviously. As it stands compression drivers mostly cruise along in a domestic environment given their towering efficiency, so thermally they'll never approach their limits here. 

Besides, I've never heard a compression driver that sounded worth having, so I didn't think about it. :-)

Remember they always come with a horn or waveguide, so what you don't like about that combo could be a combination of factors. You don't like it regardlessly, fair enough - to each their own. I feel the opposite, but I thought this was about reliability first and foremost ;)