Well...which one do you like?
I suppose it depends on what your goals are. Judo and BJJ are both great arts (when well taught). Judo tends to work on throws more often, and will likely give you a great ability to pick someone up and dump them on their head. BJJ will tend to give you awesome ground grappling/submission skills. (Note: Not the same thing as good groundFIGHTING skills, which is a quite different animal).
If you're looking for some really hard-core, street oriented Jujitsu, check out Walt Lysak's Sento Method (will get back with a web address soon). One of the PDR guys, Phil Hughes, did some work with Walt, and his ground skills are phenomenal. I can only imagine what Walt is like (though I intend to find out...).
Aikido and Uechi can compliment each other well, but most Aikido schools are a little too much into foo-foo dust and mystical powers for my taste (speaking as a Shodon in the art).
I like Judo and Bjj because they include free-style practice within their cirriculums, and dammit, I like rolling with people. But that's a purely visceral thing...
I suppose it depends on what you're looking to do.
Cannot comment on other jujitsu systems, never having any real exposure to them. I'm sure Mr. Murphy would agree that his system of Jujitsu (Nihon, yes Mike?) blends pretty well with Uechi..but I know squat about it, so I will let him comment.
In the end, find a teacher you like and that works for you (though I think you knew that already...).
You might also investigate some of the "other" grappling arts out there...Sambo, Chin Na, Shuai Jiao, ect...
Many cultures are good at dumping people on their heads and making them into a pretzel...
My .002 of appropriate denomination (no refunds, please
Defeat is worse than death. You have to live with defeat - Seal Team Slogan