Either the BT020's if you're an all year rider (there are a few of us around, easy to spot in the wet on the track on Tuesday
) or the BT010's for better grip but less life.
I have an 010 front and 020 rear. Fantastic in all conditions on the road, excellent in the rivers across Lake Esses and Gerrards on Tuesday.
Dunno about mixing different makes Fr/Rr though! May be better off getting another Mez4 Fr and then replace them as a pair when they wear out.