CV axle shafts operate a bit smoother, but are less strong and not very well suited to more than light off-road use.
I can't comment on the very early XJ CV axle shafts as I don't have any experience with either the V6 or the Peugeot 2.1 diesel XJ. However, modern Rzeppa style CV joints are generally stronger than U-joints in the same application, one constrained by physical size.
With both types strength in service varies with condition. U-joints are usually more tolerant of an occasional degradation of their optimum environment, such as a lack of grease. When they fail, it is less spectacular, reasonably easy to replace with new parts, spares are usually common and cheap.
Rzeppa CV joints do not tolerate any ingress of contaminants, fluid or solid. I have busted a few Rzeppa joints (not in a Jeep) and in all cases the protective boot was split letting in dirt and water which accelerated the wear on the ball housing and caused the ejection of one or more drive balls. It is surprising how much punishment a clicking Rzeppa can take before it fails - a lot longer than a clicking u-joint.
For me, U-joints give me peace of mind. I don't need the extra strength that Rzeppa joints can provide especially if I have to regularly inspect every pleat in a flexible boot for damage to achieve it. Pleated boots are a bad idea on anything that has to drive through forestry mud.
The
RCV joint without pleated boots are amazing. If they can truly keep out contaminants from immersion in mud, then I believe they are likely to be a good investment. Your spare shafts can be your old U-joint shafts.
In recent years the cost or replacement Rzeppa joints for cars has dropped so much that in some cases replacements are sold with new shafts already fitted. In my locality, it is now cheaper to replace an axle CV on a Honda than to replace a 760 u-joint on my Jeep.
Slightly off topic: After more than twenty years of using both greasable and non-greasable U-joints, I have finally worked out from my records that the non-greasables have lasted longer. When my current spares stock runs out I will be switching to non-greasables.