Just for the record, I LOVE the classic grips. Fits my hand like it was made for it. Also has a pleasing look, IMO for a rubber grip.
I HATE HATE HATE HATE, well you get the idea, the modern grips. The finger grooves just destroy the ergonomics for my hand. I also think the modern grips are hideous looking, and detract from the nice look of the GP.
I like the old style wood inserts for both look and feel. The hogue grips dont fit my hand. There is to much swell in the palm of the hand for me. I also had a set of aftermarket hogue grips that had the clip the holds the grip on rust up.
Classic, all the way. I have VERY LARGE hands (a Glock 21 fits my hands real well) and, so far, none of the stocks that I have tried that have finger grooves fit me at all. The finger grooves are in exactly the wrong places for me. In fact, nothing that I have tried that has finger grooves (including 3rd and 4th Gen Glocks; as much as I LOVE Glocks, I won't buy any of them made with finger grooves because they don't fit right) fits me right, including Hogue stocks.
I have the standard-size GP100 grip and the compact-size GP100 grip from Ruger, and the Hogue grip that's now the standard-issue Ruger grip. Out of the three, I much prefer the compact-sized Ruger grip (originally provided for the fixed-sight GP100 models), followed by the standard-size Ruger grip, and lastly the Hogue grip.
I've found the compact-sized grip to be effective, ergonomic and easily concealable on my 4" GP100.
The smaller standard grips on the fixed sight GP100's didn't do anything for me and kept my middle finger in constant pain. Switched to Hogues, but they were too big for CC. Switched to the larger standard grips with inserts as was used on the adj sight GP's and problem solved!
But that's just me. YMMV