Edit: I just looked, and a Tageskarte for interior Munich costs 5 Euros a day, and I would need 2 for 10 Euros. A return bus ticket would cost 17 Euros for a total of 27 Euros. Two Tageskartes that include the airport would be a total of 20 Euros, so cheaper. Is the bus any faster than the S-Bahn/U-Bahn route?
It should be about the same. At off peak times the bus can be faster. However, the S-Bahn takes you directly to Marienplatz, whereas the bus takes you to Munich central station.
Edited: I saw you want the Renaissance. No doubt about taking the bus.