Colonising Mars is easier than Moon

Mars has air, water, and had enough geographic activity in the past to make for plenty of able ores and other materials that can be of great use to future colonists. It won't be a lucrative investment for a good while, but given the proper start-up equipment and assuming we find a way to deal with the radiation (which is still significantly less than on the moon), the long travel times (for which there a few candidate solutions that could drastically cut the travel time) and the different gravity.

There are theoretical frameworks for terraforming a planet, but it would take generations, a lot of money, and technology that's not really there yet. However, it is possible, and it can definitely be done in smaller pockets of the surface area - depending on what and how many bacteria and other micro organisms might be around there, it wouldn't be too difficult to grow crops and have a proper air circulation that's not harmful to human beings.

The moon really doesn't have any of that; the main reason to get a colony going there is to have it serve as a sort of transit hub, as the low gravity there means less fuel and higher acceleration for space faring ships. Humans could never really survive there for extended periods of time though, unless we were to live underground near the poles of the moon.