It can vary with the trip. Often scenery is pretty high on the list. Sometimes sampling the local food is a factor. Meeting the local folks or other tourists can be as well. I prefer a simple route where complex turn by turn directions are not needed most days. In general I like a goal like crossing a continent or reaching a distant point. My tours have all been in the US, but I like to get away from home to start and ride toward home. I like to have a distance of at least something close to 1000 miles and longer is good. Overnight and other really short tours have generally not interested me.