Matic was brilliant at one point but that seems to be a distant memory and, for me, a weird feeling that it now looks like a hardcore purple patch. Coz before those couple of seasons, and since, he's been pretty invisible/forgettable.
That said, depends on the price. I certainly would rather Matic than Dier but it all comes to down to price and availability. I'd rather spend 40million on Matic than 50million or more on Dier to Daniel Levy, neither will take us to the next level so we may as well save ourselves a bit of cash in the process of going nowhere in midfield terms.