Mitas is the more modern radial tyre whereas the Pirelli is a very old crossply design, I'd say the Mitas should give you better grip off road but the Pirelli may give the better wear on the road.
I've read quite a bit on trialscentral where both tyres have been talked about, grip & MT43 are considered mutually exclusive terms due to it being basically a 70s era tyre. The Mitas doesn't grip anywhere near as well as a full on trials tyre but can be acceptable on the right bike
Cost difference also favours the Mitas so that would be my recommendation