I don't think there's any clear-cut answer to this one. All I can say is that I was in the same boat as you at the end of last year and went to look at a used T6 Caravelle with the options I was after (not that many around), and the finance quote I got meant that for a few quid more I could have a brand new t6.1 for almost the same as a used t6. The only downside was I'd have to wait a bit for it because it was brand new. I spent a couple of months wrangling over what to do (I'm not massively sold on the digital dash) - the spec I wanted meant the used options were few and far between and were already the 'old' model. So, I decided to order a new T6.1 in March... just in time for manufacturing to stop.
I intend to keep this one for a while (4 years free servicing/warranty extension were included as an incentive back then), so I'll be only a single revision behind for a while. Mind you, if the new T7 looks anything like the artists impressions knocking about, I won't be looking to 'upgrade'!