Probably true here as well, or as mentioned, Castrol by virtue of being most easily obtained these days(ie: Canadian Tire, Walmart, partsource). Though walmart might be a red herring since they usually put one brand or another at tempting prices.
On the topic of most found, easily spotted, anyone noticed that valvoline seems to be losing shelf space? Used to be valvoline dominated shelves, now it seems Castrol and Penzoil have taken the majority of space. Even at TSC which at one time seemed to be valvoline territory has a lot more brand variety.
Alex.