Time

Well this seems pretty straight forward, how much time does your job take from your life.

I will state the obvious and say that moving to a startup requires you to spend more time at work than a large company requires of you.
Now I know that some might say that working in a large company can be just as time consuming as working in a startup and that they don’t think people at startups work more hours than they do. And while that may be true in principle and the amount of weekly hours spent on the job will be the same, there is still a difference.

When working in a very small company, a single person is usually very hard to replace.
This makes taking time off in a startup much more difficult than in a large company.
Furthermore, if you know you are heading into a time in your life where your time at work will be diminished like finishing your Masters degree or expecting a baby. Large companies can usually accommodate these changes with relative ease, you do less time and the work load splits evenly.

The possibility of slowing down and investing less time at work at specific periods in your life will always be easier in a large company where there are many people who can cover for you.

When you are approaching the decision you need to look ahead at your life and say:
how much time will I be able to invest at the job a year from now?

Risk

By risk I mean the threat of losing your job, this is a very tricky subject.

Large companies provide a security blanket that allows good engineers to keep their job even if their entire team is downsized. Furthermore even if large companies encounter heavy losses and decide to close shop; it is still a very lengthy process that may take months or years to complete.

That said. Small companies have the advantage of close personal relationships between the management and employees which may mean that a person is less likely to be fired even at the expense of some discomfort to the company.

Risk assessment in startups is very hard and not being an expert on the subject I don’t think I can offer a lot of insight into the process of evaluating risk, however, I will say this

Before deciding a startup is the place for you, sit down with the CEO and have a talk. Technology alone doesn’t make successful startups, the people steering the boat need to be visionaries with mental flexibility. The kind of people who aren’t afraid to fail, have faith in what they do and at the same time are capable of changing direction quickly enough if needed.

I think the last point is the most important and most difficult to assess when choosing a startup.