For those considering a river cruise...I offer these thoughts. This was our second Viking trip in the early Spring, and we chose it mainly for the price reduction. There are pros / cons to going at that time: pro: cost, fewer crowds, but the biggest con is summed up in one word: TEMPERATURES. We were gone 10 days from March 22-31, and it was cold, 30-40's mostly, maybe one day of low 50's in the afternoon.
When planning the trip, I searched weather history, and reading upper 40's low 50's doesn't seem bad. Wrong. Most of the tours are in the morning when it is much cooler, and many of the tours involve walking outside with a guide. The guides and tours are really interesting, as is viewing the villages, churches, etc. But unless you really love cold weather, standing outside with a cold, brisk, damp wind cutting into you, when it is 30-barely 40 degrees, seriously diminishes enjoying what you are seeing, or hearing what the guide is saying.
Also the boat has this beautiful upper deck and chairs. What a neat way to view the countryside, as you cruise a river. But again, not in those temperatures. It was too cold to be on the sundeck more than a few minutes while cruising.
My husband and I are already signed up for 2 more Viking tours, but we will never take one in March / April again. We'll spend quite a bit more to take one in warmer temps, but the pay-off will be that we will get to enjoy the outside tours and be on the upper deck of the boat. Not to mention, seeing flowers and colors of green, instead of winter dormancy.
The cabin level or having glass doors is really not important...Nearly all the cabins are the same size, and so little time is spent there. Often at docking you are alongside another boat, or pier, so curtains are usually closed anyway when in the cabin. Also having a cabin on the same level as the restaurant is not a plus. More people going up / down the hallway. We personally enjoy a lower level, and towards the end. Our room had a nice window, but it was away from traffic activity, and we were able to hear the lull of the water around the boat.
We've not tried other river lines. I can't imagine them being any nicer. The Viking staff really does seem to try to exceed guest expectations. They do a fantastic job.