Well, first, I'd test both. If both work fine, I'd give preference to the Sansui. The
Sansui is 60WPC and the
Harmon Kardon, 20WPC. The Sansui will give you more overhead. Plus, the Sansui has those super pimp mechanical VU meters.
I'm not sure that either would be considered highly collectible though. I don't see a lot of value in antique receivers that aren't tube, Marantz, McIntosh, or similar. I'm not much of a picker though, so I could be mistaken.