Holland America. Almost no kids or party-hearty 20-30 somethings. Just us old people who enjoyed a relaxed pace.
That was just last month: Greece, Egypt, Cyprus and Turkey. I'd definitely choose that line again in a heartbeat. Our friends took it another 10 days across the ocean into Orlando, Florida. I'm considering doing that next time.
For European river cruises, I liked Gate 1, and Viking. Highly recommend those. We went 1,000 miles from Amsterdam, through Germany, hit Austria and Budapest.