Having been through the startup song and dance more than once, I can give you a single data point: what motivates me.
1) I prefer to work with small rather than large companies because of the opportunity for autonomy and to understand and be involved in the business as a whole rather than just one tiny corner. But upon interviewing I have to be convinced I'll get those things.
2) How low is the salary? I don't expect Google salaries from a tiny startup, but I won't take less than what I see as market rate for small companies, either. The opportunity cost is too high, and I've got enough experience to know that the expected value of all those stock options is exactly $0.
3) I pick jobs in part based on what I want to learn next. Sometimes those are technologies (a language or framework); sometimes they're developer skills (get better at code review or devops); sometimes they're soft skills. You need to be willing to hire people who don't already have experience in all the things you expect them to do. And you need to either be able to give them mentorship or the space to fail until they learn those things.
4) What's the commute like? A five minute difference in commute won't be the deciding factor when choosing between jobs, but I'll never take a job that requires more than an hour each way; and a 10-minute walk to work is incredibly appealing. Even better, allow me to work remote at least 3 days a week, with zero commute and more control over my environment (see next point). And if you're open to fully remote work, you can find excellent senior developers in Nebraska, Argentina, or Poland, whose expectations around work culture are similar but whose idea of an excellent salary is half that of the Bay Area/NYC/Seattle/etc.
5) What's the office like? I've resigned myself to the fact that almost no small companies have anything other than an open office these days. Poke around HN's archives a bit to find out what the majority of engineers think of open offices and why. If you can offer private offices, small team offices, or even cubicles, highlight that in your posting to get developers beating a path to your door.
6) What are the hours like, and are they flexible? After doing this for 15 years I can say with confidence that while I can do a couple weeks in a row of more than 40 hours during crunch time, it'll take either a week off or 6 weeks of working 40-hour weeks at 50% productivity before I'm back up to full productivity. Too many startups try to push their developers at a 60-plus hour/week pace and quickly burn them out. I won't even consider that job any more. I value my health (mental and physical) much more than any job.
There are probably a few other things but they're not coming up off the top of my head. You'll notice that none of the above points are especially "sexy" - they're mostly about offering day to day quality of life that's better than I can expect elsewhere. Junior developers who are new to the industry may be dazzled by the idea of a dream team and exciting new problems and omg equity! But most of us who have been around the block a few times just want a sane working environment and reasonable compensation at a place where we won't completely stagnate.