Aix-en-Provence to Avignon

I don't know about buses, though I'd be surprised if there was a bus better than the train for this route.

There is a direct TGV from Aix, though the AIX TGV station is outside of town.

yes, Aix to Avignon

From your question: "It looks like all trains travel to Avignon from Aix via Marseille."

No need to go via Marseilles. Aix to Avignon in 20 minutes via TGV--that's Aix TGV station to Avignon TGV station. Add for the time to get to and from both TGV stations, which are out in the country.

Or to bypass the TGV stations and go town center to town center, it's about 1hr 15mins. Either way by-passes Marseilles.

You can find all schedules here

http://www.bahn.de/international/view/en/index.shtml

Note carefully that Avignon TGV (TGV = high speed line) is a different station than Avignon Centre; same with Aix.

Thank you so much, this is very helpful!

Glad to help. Even though it's technically the German rail site, it's the easiest-to-use site for rail schedules in most of Europe; you use it to get schedules, not for buying tickets.