Mr. Resin Surfacer - use SPRAY or PAINT ON type?

I use the former one, I think its easier to get a good coat than to paint it on. Although I can see how it would be easier to paint it on if the doll have small details

 

I know this is an old question thread, but I wanted to add my two cents in for those who may come across it with the same question. I found that you may be needing both types of surfacers/primers. Spray on type is ideal obviously for most of the parts, although a paint-on type would be needed to prime and coat the insides of joints, sockets, etc, that would otherwise be too difficult if not impossible to spray. For such a purpose, messy isn't a big issue since they won't be showing anyway, so paint to your heart's content and make sure to get a nice coating to avoid any issues when molding your parts.