Going to be honest here. Based on CURRENT gameplay and NPCs functioning at 90 percent of what people can do, I will most likely fill my ship slots with NPCs. That said, the reason I would do that is because I would much rather have an extra ship along than someone manning a gun. This is especially true if having the extra ship along either increases profits, or helps raise the overall chance of success for a particular mission. They are still "coming with" but just on a different ship.
Now, that said, I expect gameplay to change from now to release. If it changes significantly to the point where being an extra on a crew is fun and rewarding (I don't find it so right now), then heck yes, crewed with people if I can, NPCs if I can't. However, I would still want for someone to take a different ship if profits/success rates warrant it.
For example, we have a group going out to mine rocks. We are scheduled for a 3 hour tour...I mean mission. If we have the protection available to us to cover another Orion and I have the choice between giving up two people on my ship in favor of them bringing their (or someone else's) Orion, I would want them to come on the other Orion and I will hire NPCs. If I have a slot on my ship being currently crewed by an NPC and someone else who only had a Mustang wanted to come on my (miner, explorer, salvager, whatever) for a mission that was going out beyond the operational range of their ship, I would rather have the live person. If they had a Freelancer that they could bring and we were iffy on the hauling or protection, I would probably want them to bring their Freelancer instead.
It all comes down to what is best for the mission and the group. Ideally, bring your Test friends and make lots of money. If you can't, buy...I mean hire some NPCs, and make money until your friends are free.