I rode the F650GS for a few years and I have the Versys 650 at present.
There is some feedback about the latter in this thread:-
And there is an amount of comment on the F650GS in the BMW tech thread, but not a lot, so far, about the G50GS.
You probably know that the G650GS has gone back to the roots of the F series after a few years when BMW did not produce a single cyl engined bike.
So, that engine is extremely well proven.
Either of your short list will do a good job, so a lot of your decision comes down to the usual factors of where and how you intend to ride and the other factors, such as "which one you like better".
+ do you prefer a twin or a single cyl? Choices to be made eh!
Try to get hold of each and take it for a ride - the longer the better!