I'd be grateful for some local parkrun advice.
I'll be staying at Kingston, near Lewes, soon and plan to do a parkrun. Priorities (in order) are: not too congested (given current covid situation); ease of parking; surface (the firmer the better); distance from Kingston.
Peacehaven and Seaford seem to be the closest, then East Brighton. But I'd be happy to head further into Brighton or Hove if they offer better options.
Seaford is all road, completely flat and has plenty of parking. That would be your best bet. Peacehaven is part road, part off-road. East Brighton is all grass.