My observations/opinions:
EZ-Curl Bars are good... so are Dumbbells... (straight bars can cause problems, especially for some -- depending upon skeletal structure)
Usually the best grips for saving one's elbow-joints while doing curls are:
(with EZ-Curl/Triceps-Bars, or Lat-Bar used up-side-down with a low-cable)
\________/
\------/
\-/
|------|
|-|
(with EZ-Curl-Bar, wrists bent/loose/flexible*)
/------\
/-\
(with Dumbbell)
/
|
\
* To work forearms along with biceps, use a relatively light weight, & keep the wrists locked (as keeping the wrist loose/flexible pretty-much takes the forearm muscles out of the exercise)... note that the forearms are also worked along with the biceps when using a hammer-grip style (|| or, with dumbbell: |), & a fairly heavy weight can be used without undue stress to the wrists
Hope this helps