First, it depends on your risk aversion. If you have kids to support, you usually can't afford take as much risk - so the "startup salary" might not even be an option.

But assuming you can afford the risk: Make a guesstimate about the expected value of an exit, add some risk premium, and compare. e.g.

If you assume $1B exit with prob. 3% (and no other outcomes), the expected value of the company is $30M. If you are offered 2% of the company over 4 years, that amounts to $600K or $150K/year at most (probably less, given tax considerations, exercise price, etc -- but let's assume the maximum).

Now the risk premium: you can be fired at any point, you are 97% likely to only be left with salary, and there's the opportunity cost (if something good comes your way, you'll have to choose and essentially forgo the equity). Altogether in my book, that's a 75% risk premium. It's down to ~$40K/year for the equity value.

So, in this case, I'd value e.g. $120K "no equity" with $80K "with equity".

Now, if you think the company is going to top out at $100M at 3%, I'd value $120K "no equity" as $116K "with equity".

When you look at it this way, it is clear that in the vast majority of cases, you should treat options/RSUs as lottery tickets or potential bonuses, but not much more.

Unless you happened to be an early Microsoft, Google or Facebook employee (what's the probability of that?), you're almost surely better off with high salary.