Better to hire the best you can by other criteria and let the chips fall where they may.
The reason why is that people that you hire early and that put together the core of the company will have a bunch of extremely important knowledge that will be very hard to transfer to another new hire. If a start-up spends a great deal of time replacing people that were hired and that left just as fast that would seriously affect continuity.
It is for that very reason that in later funding rounds it is not unusual to ask these people to sign on for an X number of years in return for some stock with a vesting period.
Perhaps more apropos, skill is more of an unwavering quality than loyalty. The way to make a great developer loyal is to give them interesting stuff to work on and have the right culture. If loyalty is your metric, it's more effective to worry about your office conditions than to try to pick the right candidates.
I'm a prime example. At 33 I've only had 5 jobs since I was 20, so I look incredibly loyal as an employee. But there's a reason I stayed at each of those jobs for so long. I would not suffer a pointy-haired boss for a single day.