[quote name='Sleepkyng']well, i want to maintain fitness and have some fun. Meditative aspects are plenty good but overall it's for wellness.[/QUOTE]
Then here's my advice: go with the boxing. Tai Chi (as it's generally taught) is low impact and heavily meditative. If it's available, yang style tai chi is a little harder, but still far from a boxing workout. Judo and Sambo are similar in that they're reliant on grappling and throws, which makes them (particularly the Sambo -- Judo is often taught as a sport, though not always) a little more practical than even the boxing for self-defense, but most martial art classes are there to teach you the art. They assume you're working on fitness outside of class, so they tend not to spend much time on it, other than some warm up push-up and stancework where applicable. Boxing, on the other hand, is very much about conditioning, so it's geared toward drilling the basics and keeping you fit at the same time. You'll also probably get to spar earlier than you would with the other options, which may keep your interest better than, say, drilling breakfalls by yourself for three months. Lastly, being able to throw a decent punch is always a good skill to have under your belt.