I’ve used both Grey and Tough 2000.
I like Tough 2000; it’s definitely less brittle and less prone to breakage. However you can’t achieve quite as much detail as with Standard resin; edges and fine features come out sharper and better looking in Grey.
If your parts sustain a lot of impact you might also check out Tough 1500 or Durable.
I’m not sure if you can switch a Form 3 tank from a Standard to Engineering resin. Some discussion on that here Tough 2000 resin - they were going to do some firmware updates to ease the restrictions, I just can’t remember if they’ve been released yet. Make sure you buy a v2 tank.