I use a somewhat mixture of both, in my adult female's tank she has a cement hide that in a way acts like a rock you could say and then a branch next to it. The cement hide gets a bit hotter definitely because it holds heat just a tad better but majority of the time shes either on the log or half and half.
In my adult males tank his log hide is at the same height as hers but doesnt get as hot as her hide does, hers being around 106-108 with her branch being at 90 or so. And then his being at 95 for the log hide and then he has a branch to get higher that sits around 105 or so.
And lastly in my juveniles new tank the tiles get about 95 or so on the warm side underneath the bulb with her basking spot, that holds in heat like a rock i suppose, not entirely sure what kind of material it is exactly but it sits around 115 where the halogen 75 watt shines brightest and then the majority of the platform is at 108 or so.
In a way it probably depends on what type of light bulb and the wattage you use. The reptile bulbs definitely dont produce as much heat as the halogen does but i'd say the rocks and things like that do get a bit more hotter than the branches. However i prefer a little mix of both and depending on tank size mostly i'd have the logs/branches and rocks at the warm end.