What is your favorite, lossless image format for games (namely 2d games)? And why?
Some things to take into consideration are size on disk, overhead for converting to a usable format, and features of the format (ie alpha support).
There is no best answer, but be sure to back yours up the best you can!
I'd suggest PNG. Most software supports writing it, most libraries support reading it, it's lossless and supports alpha transparency. And it's a standard format.
And, maybe important for hobbyist 2D games, very small images also result in very small files (i.e. a 16x16 icon can be 1KB or less).
There is a best answer, and it's clearly PNG.
Good compression, supports paletted alpha, extensible (in that you can attach arbitrary blobs to a PNG), what's not to like?
I like png a lot. It has a good compression, supports alpha channels, and supports color pallets, so file sizes can be smaller. And it is pattent free, so everybody can use it.
PNG does NOT support alpha transparency, it has a translucency channel, which is different. This can lead to problems depending on how you are rendering sprites to the screen. TGA, hands down.
