Although many may argue for the factory sealed ujoint, I much prefer the spicer with the zerk installed. Many "sealed" ujoints will run for lots of miles with the needle bearings rusted almost completely away. (My '94 F150 went 60,000 on sealed units but when I changed them, they were rusted almost solid!) I've seen it many, many times. One telltale sign is a squeek or slight grinding noise at speeds below 10 mph or so. The joint may have no play or show any outward sign of deterioration but when taken apart, it's a rusted mess! Alot of drivelines don't run a harsh articulation angle so if the joint is nearly "straight on" most of the time, you may not know when its lost its lube and is corroding away. The "old timers" always told me to grease the "joints" every oil change and keep pumping until you see new grease flowing from each bearing boot or seal. I think that has been very good advice, at least for me. My '95 F250 4WD has been through plowed fields with mud frame deep, snow bumper deep, hundreds of streams and ditches with muddy running water and God only knows what else, and I always grease up good afterwards. Over 100,000 miles later, the spicers are still in service with no problems and I'd wager they have another 100K in them yet.
My $.02