almost all game engines olny use png or tga, for getting content into the game engine, once it is there it is usually converted to dds, and gets mipmaps generated for it.
There was a thread once, I can't remember if it was here or on UDK, which also talked about those and mainly about image formats with and without compression. The issue was that if you have an engine of some kind, for compressed image formats, it not only had to read the image, but had to decompress it to use in the…
TGA's, because most engines will process them much better (especially for mipmaps) and most image editing softwares cannot process/read 32bit PNG's for Alpha if you should require such a thing.
png it's realy good for space but it takes a hell of a lot time to load in pretty much all engine and compositing software as i know, maybe on render don't make any difference but don't know.