I tripped over this on wrangler forum (technically @cheezy pointed me at it)
But I. Figured it would be useful here, it's TJ focused but the attached graphic has some JK info as well.

There are actually seven u-joints on our TJs, two on the axle shafts and five on the front / rear driveshafts.

Two front axle shaft u-joints:
The factory u-joint on standard (non Rubicon models) is a Spicer 5-297. A highly recommended upgrade is the Spicer 5-760x which is sealed and a stronger, more durable direct replacement. Rubicons came from the factory with the Spicer 5-760x u-joint which was specially designed for the Rubicon at Jeep's request.

Driveshaft u-joints:
The stock driveshaft u-joints are Spicer 1310. There are three u-joints up front and two in the rear. A highly recommended upgrade is the Spicer 5-1310x which is sealed, as well as a stronger and more durable directly replacement upgrade for the standard Spicer 1310 size u-joint.

The TJ Rubicon uses different driveshaft u-joints, be aware they vary between 2003-2004 and 2005-2006 Rubicons. All years of the TJ Rubicon came standard with the Spicer 5-760x front axle shaft u-joints.

The items in red circles are treated greasable joints for the rubi, the non circled ones are non-greable.