Okay, first off, both are completely different games, yeah, they're puzzle games in first person perspective using a gun to solve puzzles, but both have entirely different mechanics, setting and puzzle mechanics.
While in my personal opinion, Portal is the better, I do played The Ball when it was a UT3 mod, I think it was the version where they added the zombie gorilla and it's a very interesting game.
You get to kill lots of mummy things or zombies or whatever they are and the puzzles are quite clever, obviously the graphics are way better than Portal's, because in the first place, it uses the Unreal Engine 3 and second, you're not confined in room tests, you get to traverse pyramids, you get to see places filled with lava, plant filled caves and it has way much more variety in the environments than Portal.
And the mechanic of the artifact you use to control the ball is quite similar to the portal gun, except you do 2 things with it, you hit the ball and it lauches to wherever you want and the secondary button acts like a magnet and attracts your ball towards you.
Maybe it was because it was in mod state or beta or whatever, but the only thing it lacked was a villain as likeable as Glados or something, although at the end of the mod it hinted the presence of a villain, but the game was rather incomplete at that point.
But you can't compare it to Portal, to me, Portal is way better, but The Ball as a lot of potential and, as a mod, it already felt like a commercial game and I never felt I was playing someone's basement project, I felt it was like beta testing a full commercial game.
EDIT: In fact, I recorded a ahort video a year ago, when I played the mod http://www.xfire.com/video/c29ab/