I find Heathrow much worse. For one thing except when connecting from the few domestic flights you always have to not only re-clear security but also pass their useless conformance check. Second the ways even inside T2 can be pretty long - the worst being a connection from T2B to T2B that requires a walk to the main terminal and back.

FRA I honestly don't find too bad. The fact that you have to pointless reclear security when going to or from T2, T1C and many itineraries involving T1B messes things up but otherwise FRA isn't too unpleasant as far as airports go.