If the £25m clause is true it's a no brainer. IMO Denayer was the better of the two at Celtic, but then again, there was a time when Rooney was better than Ronaldo for the rags, one went on to fulfil potential and the other went bald.
We only have 1 CB for the future under Pep as far as I'm concerned, and it's Stones. Going forward we need to find at least 2 more who are front line and a 4th who would be a youth prospect.
I'm not sure that VVD will be one of the best defenders in the world like some think, but I do think he's good enough to be one of the 3 main defenders.