best gta 5 graphics mod?

NVE hands down, constantly updated and its not just a reshade, it actually mods game files so yes, it gets pretty hard on your cpu and gpu, but, if you have the PC to handle it, go for it.
You can try the Low, Medium and Ultra presets on ENB, and additionally you can also use the performance mode, giving you a boost on fps but turning down some features.
Test them and see which one suits you the best.