I have direct experience with the NiteIze 3x5mm LED upgrade, the luxeon based Terralux TLE-5 and the Seoul based Terralux TLE-5EX. The NiteIze, which my father bought, is the dimmest of these three, and I would personally not purchase it. The TLE-5 is nice, very very similar in color and brightness to my 2AA mini Magled. The TLE-5EX is the brightest and whitest of these three, I consider it a very worthy upgrade to the minimag and makes for a useful light. I don't have personal experience with the cree version (most recent) of the TLE-5EX, but from what I've read, the beam has a much more defined hotspot and slightly less output than the seoul (SSC) version.
If i had to do it all over again, I would first try to purchase the SSC version of the TLE-5EX by looking for a store that still has them in stock. Failing that, I would buy the cree version.