How much time you have is the main consideration when deciding whether or not to get a puppy or an older dog. Raising a puppy can sometimes feel like a full-time job. They have a seemingly endless amount of energy and require a lot of attention when it comes to house breaking and training them.
You can count on it taking several weeks, if not longer, to properly "potty" train a puppy. Plan on lots of middle of the night trips outside, not unlike a newborn baby's schedule. An older dog may already be house broken and crate trained, and if they aren't, they'll likely be a quicker study.
Adult dogs are also more likely to be through their destructive chewing phase. Finally, animal rights advocates will tell you that there are more adult dogs that need adopting, which is always something to consider.