Which device makes for a better digital music source? Computer or streamer?

Very interesting! thanks rossb....

The definitive answer without question is:  it depends.   Like most things the devil is in the details and generalizations do not carry much weight. 

Stands to reason streamer generally going to be superior to most server/streamer combo and far superior to general purpose computer. Noise is the enemy, segregating streamer from server or computer results in least amount of noise just prior to dac, certainly one of the most important links in network chain.

I really prefer no rendering taking place within servers, in this way they become simple network devices, minimize signature on sound quality.

Streamers are computers. So is your iPad and phone. Using a computer that's designed for streaming can be better than a laptop or desktop but there's no hard and fast rule. I'm using a NUC running ROCK if I'm going through Roon. I can also connect my speakers to my network and stream direct to them. I use a tablet as the controller. 

Streamers are indeed computers, but run relatively few processes which means less noise generated. Add better rendering capabilities vs most computers, servers/streamers, wins on two counts. Streaming dacs are also nice, foregoes external rendering which can be advantage.