Trip is in 3 weeks, still no transportation for a day trip from Geneva to Chamonix. Is renting a car for the day a good idea, passable roads? Anyone know any reputable small bus transportation companies?
Most of the buses are a tad pricey and mostly serve to take people from the airport to Chamonix in vans. Renting a car is OK, I've done it to get into the French Alps. I guess I would prefer to spend at least one night.
I also would prefer to sleep in Chamonix, if you don't really need to sleep in Geneva. For taxi services not necessarily departing from the airport, see www.chamonix-transfer.com. Trains to Chamonix through Switzerland, around Lake Geneva, take 3 hours with 2 connections.
rome2rio says take the bus, 3x day, 1.5 hours
The road from Geneva to Chamonix is very nice! Don't worry about that. I have driven to Chamonix from Geneva via several routes and I have always found the roads to be excellent.
It is a fairly quick drive to Chamonix and there is a huge parking lot when you get there, right behind the Aguille du Midi gondola station. From the lot you can walk to everything.
A car will get you there faster than any other form of transportation and you won't be tied to a shuttle bus or train schedule. It's good to have that flexibility when you only have a day.