We did the Delos tour through Virgin and wouldn't do it again, even not through a cruise line. We thought for sure the ferry was going sink because one was out of service so they jammed everyone in one boat. Once arriving on the island it was absolute chaos. After finding our guide we walked for what felt like forever through a wild crowd of people, especially very large groups that just trampled everyone else. Our guide was incredibly monotone and boring, no energy whatsoever and there was absolutely zero shade.
We have done many excursions through Virgin and a lot of have been great, we just didn't think Delos was great at all.