I honestly prefer oil.
I’ve used grease on my Sigs—mainly because of that infamous article/post that explains how your Sig will disintegrate if you see bare metal on the frame rails. But I feel like the thicker, more viscous medium tends to slow down the slide. In particular, I noticed this with one of my P225s/P6s. Using TB25b grease, I would occasionally have a FTFeed from slide lock. Went back to oil, and the slide seemed a lot snappier going into battery (from slide lock) and never hung up.
Granted, the recoil spring was pretty old in that P6, but I don’t think there’s any question the slide was moving slower with the grease. Now I never had any issues while firing (even using just grease) but… I tend to think slowing the slide down isn’t really a good thing?
At the end of the day, oil is just more slippery than grease (at least the grease I’ve used). And I think most guns were probably designed to run with oil. Plus, I kinda think the whole aluminum alloy frame wear thing is a bit overplayed. After handling some raw machined aluminum parts… it seemed pretty damn tough to me.