For client projects, if you've worked with the LAMP stack for a few years and are thinking about making a transition to the MEAN stack, I suggest transitioning gradually. For example, start by doing most of your front-end work with Angular. Once you're comfortable with that, you can move on to node and express, while still using a traditional SQL database. Once you're familiar with node, you can move to Mongo. If you take it one new technology at a time, you can build your skill with each new technology without worrying about falling behind on your deadlines.
Alternatively, if you are working on a project in your spare time, there is no harm in going straight for the full MEAN stack.