I've replaced 3 driveshafts worth of U-joints in my life, so hardly the expert, but this has been my experience:
The first was in my '02 F-150. I used a combination of a ball joint press and a bench vise. One had gone completely dry and the needle bearings had lost about half their mass to red powder and sounded like a paint can shaker full of meth addicted squirrels. 2 u joints took me most of an afternoon. The second was the original rear driveshaft in my TJ. Again, I used a ball joint press and it took me about 2 hours to do 2 u-joints, and I had to beat the piss out of the yoke ears at the end to get the u-joints to move freely. Last year I paid a shop $60 to replace the u-joints in my front axle shafts because I was in the middle of an axle swap and regear project and too busy to mess with it if it was going to go like the driveshafts I'd done.
Then, thanks to some forum posts, I learned about the hammer method. In February I did all 3 u-joints in my TJ's front driveshaft in about 25 minutes with a couple of sockets and a 3lb "Engineer's Hammer".
I'll never go back to the press.