I have done it both ways (I do U-joints with the DS on the car, so I preface my post with that perspective). The 4# hammer works fine if the caps are moving easy. I really like the C-clamp method though, and once the caps start moving, it doesnt take long for them to pop. I have bent a couple 6.5" clamps doing this - the industrial C-clamp in my ball joint press tool kit is much beefier and would work a lot better.
If you have zerk fittings on the new joints, install them correctly (there's a strong and weak side - this is a nuance not many people bother with, but why not do it right).
Good luck.