PNG
- Smaller file size (lossless compression)
- Less control over transparency since it’s not stored as a separate channel.
- Modifying transparency is a pain in the *** in PS.
TGA
- Larger file size (can use RLE compression, is lossless)
- Full control over transparency, since it has a discrete alpha channel.
- Modifying transparency is easy in PS.
TIFF
- Large-Small File size (can use compressed or uncompressed, lossless)
- Full control over transparency, due to discrete alpha channel.
- Modifying transparency is easy in PS.
PSD
- Usually, huge file size (contains all info as layers, as well as channels for each layer).
- Full control over everything, if it’s a layer.
^ The only differences that matter.
Compression and size makes no difference whatsoever to your runtime game speed, since everything is uncompressed then converted to DXT/BC7/RGBA format anyway when imported. TGA is the preferred format for most people since it has a discrete alpha channel that you can bring into something like PS and modify it there, and since it’s uncompressed it’s also faster to open and save (not that that’s an issue for modern PC’s usually), AND textures can be rebuilt faster in UE4.
File size only makes a difference to the amount of space your EDITOR project takes up on disc, NOT the packaged game. For consistencies sake, I’d stick to TGA personally, but TIFF is a good format if your conscious of source control / disk space.