I'd say the 814XL. I have one myself. I also have a 514XL (not XL-S) and love it but the 514XL-S doesn't allow for manual metering. Only exposure lock. Also the 814XL has a manual exposure, a wider and longer lens, slow motion which is nice and two different shutter angles (150º and 220º) which is EXTREMELY useful for varied lighting conditions. Also just a bit more robust in my opinion.
Both are solid in the end though. And both will meter all those films correctly although if you DO use 500T, only the 814XL will meter it completely correctly although not a huge issue with Vision3 film.
I shot the second half of the below video (the sledding day) with my 814XL and 4k scans by Pro8mm with Vision3 200T.