A variation of the above theme - Land, Small Ship, River Cruises is my preferred order of tour type.
Land - provides greatest freedom, diversity of sights, you stay right in the heart of the things you came to see.Small Ship - provides more diversity of sights than river cruises. Your hotel (the ship) moors in the port or just off the port, which makes seeing things on your own more difficult than for Land toursRiver Cruises - provides the least diversity of sights because typically all cities along any given river are very similar.
The only benefit to the Small Ship/River Cruises over the Land tours (in my opinion) is the unpack once (if you ignore any pre or post cruise stays prior to or after the cruise portion). For me, the pack/unpack isn't a big deal since Tauck handles and pays for all of the luggage handling during the tour.
My friend just completed a Viking Ocean Cruise of Iceland. The ship had 700-800 guests. The Tauck ship I was on had 135 for our Iceland tour in early July. When both ships (Viking and Tauck) do pretty much the same thing - transport you to the next stop during the night (mostly), why would anyone opt for the larger ship?
We want to take a land tour of Iceland next time
I've taken at least 10 river cruises, have had to negotiate going through other boats while docked and to be honest don't remember any difficulties. I usually do a river cruise and land cruise every year and love them both. Like British the packing and unpacking doesn't matter as I use cubes and never unpack, I bring a large empty cube for laundry of items I don't get laundered during the trip.
I use the dual sided cubes- clean cloths on one side and dirty on the other.