Mint should be grown in its own container: Most mints are invasive and aggressive, spreading rapidly by runners; the advice on them as companion plants for MJ is grow them in separate containers and place the mint around MJ's container. I bought Lemon Balm mint (also commonly known as Melissa). Am also going to get some Spearmint and Peppermint to try, as well as other easy to grow companion plants. Mints are perennials, so you need not keep re-planting them. When they die down after warm season, they will spring back from their roots when winter passes. Some mints species are better adapted to colder climates. You can Google for more information on the many different subspecies of mint.
Website of Royal Queen Seeds lists several different companion plant species for MJ, w/ information about what particular benefits these companion plants offer to MJ.
On another forum, someone said he'd planted chamomile (he did not specify whether it was low growing 6" - 8" tall Roman chamomile or the taller 12" - 24" German chamomile) in the same container as his MJ and said he noticed a definite improvement in flavor as compared to same strain MJ grown w/o chamomile. Plus, the presence of chamomile in the same pot as MJ did not seem to have any detrimental effect on the MJ's growth.