I dunno.
I had once a Takahashi FCT-100 - considered the BEST 4" telescope of all time, heck, even considered the best optically of ANY refractor before or since. Yes, it had a reputed Strehl of 0.998 (call it parity really) - absolutely diffraction limited in every sense of the word. Also, VERY rare telescope (I paid a ransom for it). A telescope Roland happily tips his hat to. Only downside to it was it was pre-MC days, so the contrast wasn't as good as recent offerings (but still better than many!). Tak still makes a limited custom offering in the guise of the FCT-250 and FET-300 - both telescopes that I recall costs in excess of $100,000 (and come with their own custom mount, installed by Takahashi personnel).
It is both a visual (mind blowing) and imaging scope, as it laid the foundations for the FSQ legend.
So, as 4" goes, FCT-100 hands down. It is legendary, though many have not even ever heard of it.
For modern renditions for imaging, of course the FSQ-106N cannot be beaten. The FSQ-106ED may have slightly better correction, but I, and many others, feel the contrast and colour rendition of the N better to the ED, plus many of the N's can be found with better optics (higher Strehls) than the ED's.
I think for the larger refractor apertures, the Tak TOA 130 and 150 are right up there, but Roland and Yuri sure give them a VERY good run for the money and surpass them in many ways. The Tak FSQ130 is an unproven beast right now, so the jury is out on that one.
Mirrors? They hang on a wall... I know NOTHING about them, as my ugly mug tends to rack them
