World Showcase is most crowded on weekends and later in the day. Unfortunately, those are also the times when it is the most fun.
I find that, with the rest of the parks, the experience is pretty much the same regardless of the time of day / week / year. So I always try to go when the crowds are the lowest, and it usually works out well. A ride is ride, whether it's 9:00 a.m. or 5:00 p.m.
But there is a reason why the World Showcase is a ghost town in the mornings. Often, virtually nothing is open at that time; and even when things are open, few of us feel like drinking and eating at that time of day! When I have gone to World Showcase right at 11:00 (when most things tend to open), I've found the experience to be kind of empty.
I think that the best that we can do is avoid Friday and Saturday nights and try to find a time of year when Disney is not as crowded (to the extent that those even exist anymore).