On A/V receivers, it would be a trade off in my opinion with Marantz having an edge on overall clarity and sound, where Onkyo would have the edge on slam and being able to drive more difficult speaker loads.

With integrated amps either would be a mistake. You would get much better value from an integrated from the likes of Arcam or Creek. I don't know what Onkyo has to offer in integrated but our Marantz dealer was disappointed in the Marantz and has never carried them. I have heard pretty good things about the Marantz monoblocks and they are priced pretty good for monoblocks.