Which one is going to be better depends on the monster’s physical resistance. I don’t really know much about d2r, but I heard there are sunder charms, not sure if they work with summons but if they do, that’s a point for reaper’s. Also, usually on a pure summon Druid you’re going to want at least one aura but preferably 2+, so it depends on your Druid’s gear as well.