I don't really know what mod to use since these both definitely have different takes on the same exact thing so I assume I can't use both. Is your mod a simpler version, or higher quality when specifically dealing with diesel tech? Does this contain better compatibility with other mods like ad astra or create add-ons in general?

Mod here: https://www.curseforge.com/minecraft/mc-mods/create-industry

cdg is simpler, imo higher quality and has better compat, many people say cdg is worse, many people say tfmg is worse. cdg is more creaty, tfmg is not as much creaty. tfmg has more content, uses steel and is very complex. You can use both as long as you tag fluids from tfmg with for example forge:diesel since tfmg isn't tagged that well.