You should have both......
What species do you have? Alot of montanes require less D3 dusting then the other species do.
Young chams, I dust with calcium every/every other feeding and if only using a UVB bulb(no sun) dust 2x a month with D3. If your cham gets sun every day then you can dust only once with D3 or (species dependent) not at all as long as ur feeders are well gutloaded.