Next door, there are another three guys, eating ramen, etc etc.
Now, it seems to me like the three guys behind Door #1 are very similar to the three guys behind Door #2. However, in one case they're all co-founders, and in one case they are two co-founders and a first employee. Those are very, very different statuses for the third guy. The third co-founder gets mentioned in press hits about the company. The third co-founder can call himself a co-founder, a status of value in an industry (and society) which is sometimes obsessed with status. The third co-founder cannot get excised from the cap table without that being mentioned as a subplot in the eventual movie.
The first employee will not usually get mentioned. The first employee gets no social status of particular esteem. The first employee will not have a seat at the table -- literally or figuratively -- when the eventual disposition of the first employee's equity is decided. The first employee's equity stake is approximately 1/6 to 1/40th (or less!) of what the third co-founder's was. Well, theoretically. 0.5% is 1/40th of 20% in engineering math, not in investor math, because investors can change the laws of mathematics retroactively. 0.5% of millions of dollars is sometimes nothing at all. (This is one of the least obvious and most important things I have learned from HN.)
If you're good enough to be a first employee, you're probably epsilon away from being good enough to be a third co-founder. There may be good reasons to prefer being an employee... but think darn hard before you make that decision.