Depends, traffic can change depending on what mods you use, ect. Different supermods effect the rate that traffic spawns, ect. Another factor is what year.
Early war you will find lot's of invasion forces. They first hit the Phillipines. If you start the way out of Manila just head north to Lingayen gulf. Take time to study history a little on line. This is a good map that shows the paths invasion forces take and also good for battles.
http://www.historyanimated.com/pacificwaranimated/ Take Java for instance, in Feb of 42 there are many invasion forces.
I prefer RSRD, a mod that corrects the traffic layers, but it cuts down on a lot of single traffic. However, I prefer the large correct convoys. Many convoys have 50 plus ships.
If you're playing stock, ships spawn pretty much anywhere at anytime, that's why I prefer mods that correct traffic. A good thing to do is sit in a narrow strait, ships much easier to find.