best for Maya is MayaIFF, in pixel dimensions of 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, .. and so on. it means that texture of 513x512 would be quadruple times less effective than 512x512, because first one occupies more mem.
yes, You can use TGA/TIFF but Maya them converts to internal format, thus consumimg extra CPU power+mem+time.