I would only ever fit 4 winter tyres.
Dangerous to mix tread patterns and rubber compound, which can lead to some very unpredictable behaviour.
I could already tell difference when I had very soft Dunlop Sportmaxx RT on the front and very hard Pirelli P7 on the back and they are both summer tyres so only main difference was rubber compound.
Same goes for symmetric, asymmetric and rotational tyres as they provide quite different performance, though that is less an issue if you got at least the same on the same axle (all long as they are all summer, all-season or winter tyres).