Letting combat power aside, let's compare Golden Experience's powers against Crazy Diamond's: who's better to save a life?
- Josuke has the following advantages:his powers won't generate pain, extreme amounts of pain may cause death so he's got an advantage here. He can also regenerate a person from being dust if doing so right away. Giorno can't do that since he only replaces damaged body parts. Also Giorno's rather suited to replace lost body parts. Imagine a person whose body is beaten bady with a baseball bat. Josuke'd have zero trouble to heal him, but Giorno can't just replace those body parts unless he starts to cut them off.
- GIorno on the other side has a great advantage regarding illness, Josuke can't heal an ill person but Giorno may create a new liver for a person dying of hepatitis or cirrhosis. However a person with a tumor in the brain is beyond saving for these two, since Giorno would probably kill the person while replacing that body part. Regarding poisoning... it's a bit more complicated. Josuke has never been shown treating a poisoned person, but Giorno has shown the capability to generate serums to counter a snake venom. So by lack of feats that's a point for him.
EDIT: after reading most of the answers I gotta admit I love how Araki managed to manipulate both characters' powers. They may serve a similar purpose regarding healing during parts 4 and 5, yet there are so many differences in versatility between them.