An EZ-bar is very forgiving on the wrists if you have any problems.
EMG studies show greater muscle fiber activation with straight bar curls, but IMO, it's more important to consider one of the golden rules of building muscle: BODYBUILDING IS A VERY INDIVIDUALISTIC ENDEAVOR.
Different people respond differently to various aspects of drugs, nutrition, and training; despite what scientific studies may suggest.
You may ask ten different people what works best for them and get ten different answers - all of which, are true.
If you're curious and serious, it's probably worth experimenting to find out for yourself.