YYZ is certainly not the worst, much better than LHR, IAD and JFK. Now if only AC and the Canada Immigration service could better co-ordinate arriving connecting pax (as per YUL) my major gripe will be solved.
Aside from the loooong hikes you have to do and the "shopping experience" that BAA inflicts on passengers, connecting at LHR is actually surprisingly efficient and well organized.
As far as signage there's basically nowhere you can stand in the airport and not be able to see a purple "Flight Connections" sign directing you to where to go to make your connection.
I've connected quite a few times in YYZ and I always spend 20 minutes wandering around lost trying to find where to go. The last time I asked someone for help he turned out to be equally lost. And this was entirely within T1, no bussing involved.