LOL. +100 as well. Super.
I have done a lot of texturing for gaming including rendering testing.
TGA or PSD or TIF???
In the old days…NWN1 it was TGA because it had 4 channels…RGBA which made it excellent for gaming for the alpha transparency.
These new days TIF (not UE4) and PSD (Yes UE4) are better in my opinion for a RGBA file since they are lossless formats and can be read by these new engines. PSD has some nice added benefits.
These 4 Channel Textures are really only useful in game design for things you actually must control the alpha transparency directly in script/code. That is about it.
So let’s say for the sake of argument…5% of your textures. For UE4 PSD all the way.
PNG
Super nice lossless format that has built in transparency. Some game engines have poor PNG import techniques which require some fiddling with settings to get them working again with transparency. UE4 handles these just fine and they look awesome.
GIMP (better actually) and Photoshop export PNGs fast and very clean.
The super benefit here is very large space savings (removed runtime comment but see below for memory and BCn/ASTC VRAM compression techniques). There is no losing here.
*I have 28gb+ of textures for the game and most are in PNG with very few artifacts in rendering.
So 95% of all your textures should be in PNG format.
Please have a read of these for very good compression techniques on VRAM.
https://msdn.microsoft/en-us/library/windows/desktop/bb694531(v=vs.85).aspx
https://msdn.microsoft/en-us/library/windows/desktop/hh308955(v=vs.85).aspx
://www.reedbeta/blog/understanding-bcn-texture-compression-formats/
https://developer.nvidia/astc-texture-compression-for-game-assets