I have had one sapphire AM crystal for a Citizen diver and I didn't like it. That may have something to do with the wrong bevel on the edges creating lots of extra reflections, but maybe it was the sapphire too. Either way, it makes me wary of sapphire.
I'm a fan of keeping things original. It also helps having a number of watches in the rotation, so nothing ever gets too knocked up. If I'm doing anything remotely handy I put on an SKX007 which is banged up and I love it's battle scars. If I was a 2 or 3 watch guy then I could see the merit of Sapphire as it looks better after years of continuing wear.
Either way, I'd be buying one, I guess - I'm searching for a SBBN007 replacement crystal, as mine has scratches.
While Crystaltimes has a sapphire that fits, I am not overly enamoured with their 6309 sapphire, as it has a very bleak look on the dial. Add to that the "no AR" option (as I didn't want a blue AR look on my 6309), it's reflective as hell.
So either Hardlex (which I would prefer) or a really transmissive sapphire.