Strasbourg to Zurich

They both follow roughly the same route, south through the Alsace plain (Vosges hills on your right) to Mulhouse and Basel, then through the Jura hills and across the (relative) flat to Zurich.
I would imagine the train is more comfortable and faster than the bus and offers more departures, but requires a change at Basel. The bus probably wastes time on going into towns for stops (Colmar, Mulhouse, Basel, ??) and is cheaper.

Not sure which bus company you are thinking of (Flixbus?). Personally, I would take the train for comfort, but that is personal preference.

Thanks Chris. Flixbus. Are they the only large bus company in Europe?

You listing the towns makes me think I should stop at Colmar now. That was on my list but I cut it out due to time.

They don't stop at Colmar on the Strasbourg to Zurich route. Times were different. I wish Flixbus listed the stops on a bus route.

Some countries have large long-distance bus networks, some fewer or none. And most local city bus networks carry more passengers per day than long distance or international networks.

Flixbus is not the only large international bus company. It is the "new kid on the block". It is German owned, and sprung up and grew to be the largest network in Germany after Germany first allowed long distance buses a few years ago. It then expanded Europe-wide. It has a reputation to be cheap, but not high comfort or fast. What is known as "student transport".

The other network, which is longer established is Eurolines. This is really a marketing grouping of various national companies under one brand.
Website: https://www.eurolines.de/en/international-bus-lines/
But they don't appear to offer a Strasbourg to Zürich route.

Switzerland is one of the countries that does not allow long distance buses, only local and international ones. But that is due to change next month.

I haven't looked at the prices but I can say that the train from Strasbourg to Basel is easy and frequent and I've always just taken the local TER service which are slightly older trains but perfectly comfortable with bouncy seats and flapping curtains, and cheap. Then any Swiss train from Basel to Zürich is also easy and very frequent.

I don't think that I would want a bus for that length of journey.