I've gone through a number of primers over the years - hobby specific, automotive, general home improvement. From a rattle can, the best I've used would have to be Tamiya Fine Surface Primer. The downsides to a can are limited control, waste, and expense. I used to decant Tamiya primer, but this was generally a pain in the rear end. In bottle form, the best primer I've used until now would be Gunze Sango Mr. Surfacer 1200. Unfortunately it is even more expensive and difficult to find/import in the US. After using this Alclad stuff, though, I am sold. It sprays beautifully through my Iwata HP-C, leaving a perfect eggshell-like finish, with great coverage and no post-sanding necessary. I generally spray at 15-20 psi, and thin it 1:1 with generic lacquer thinner. It also comes in a nice glass bottle that can be re-used when empty.

This is by fare the best primer to ever go through my airbrush. Even with a slight bend in my needle this laid down incredibly smooth. It cover very light sand marks with no problem. Unlike most acrylic primers you can buff this out and really get a shiny undercoat. It is quite durable for how thin it lays down. Being a Lacquer, this can have any other kind off model paint put down on top of it (enamels and acrylics). The color of the primer is a nice flat (unbuffed) light grey. It will be the finished color on an upcoming Gundam kit.

I now use this as my every day primer. Much better than the Tamiya primer. Easy to airbrush without any thinning and spays evenly.