This generation Garp
Stronger than copper and silver
Koby is fundamentally different from Garp and that's a good thing. That's why Garp considers him the future of the Marines. Koby's different way of thinking will be needed in the world born from the ashes of the current one.
imo, Smoker has always been a closer analogue to Garp because of his relationship with Luffy, which in turn makes his dynamic with Kuzan all the more interesting. I hoped for a long time Smoker would end up an Admiral or at least strong enough to get there. Perhaps he never will (I think Fujitora will switch sides or be killed, creating a vacancy either way), but I don't think that's really important either. In terms of mentality and approach, I think Smoker has more of Garp (and Sengoku, you could say, admittedly), than Koby.