East always FL110, west always FL100. I'd go higher if I had oxygen.
Generally I fly these heights for...
1. Safety (longer gliding distance in case of engine trouble, ability to see much further & divert around weather if necessary; terrain is not a major issue, but there are a few 1-2km mountains around, so it's a safety buffer there as well)
2. Comfort (in this part of the world it's 30 degs celsius on the ground; also the air is often completely calm at these altitudes, whereas you get thermals up to ~3000 feet)
3. Fuel economy
4. The view