My experience has taught me that greasable balljoints are better than non-greaseable IF you grease them religiously.
However, sealed, non-greaseable SPICER cold-forged u-joints are the best u-joints for non-competition or extremes. Greasable u-joints always seen to have one cap and set of needles that eventually plugs up and gets no grease even if greased regularly. They let water in. The needles turn to rust-dust. Now you have junk.
There are even more robust u-joints out there thanks to truly gonzo off-roaders, but the price tag is mind-boggling; like a couple hundred per joint!
You cannot go wrong with Genuine Spicer COLD FORGED sealed u-joints. They cost a little more and are worth every penny. Anything else is a waste of time and money.