Theoretically I think there is less to go wrong with a unipivot. With an arm with conventional bearings, the clearances are crucial to good sound and smooth operation, so if you opt for a well made arm. They needn't break the bank - even the lower end Regas have good production standards (although I much refer SME Vs.
I have one system using a Roksan unipivot and have been impressed with the decent sound and lack of fuss using it.