Another really important, highly negative, combination of these factors is if you want to leave the company. If the company is public, then you can essentially leave whenever you want, exercise the options and sell the stock to pay the costs (exercise price + taxes). But if the company is private, you have to pay the exercise price + applicable taxes (which can exist even if you only have theoretical gains) yourself,…
I've been hit with this too and it's not pretty at all. If anyone else is concerned about this, you should talk with your CEO/legal team about early exercise options which can remove a lot of the risk of massive tax liabilities. From my understanding, some companies offer an early exercise option where you pre-purchase the shares and then instead of being able to buy the shares after they've vested, the company inste…
The amount you would pay for restricted stock is exactly the same as what would otherwise be your strike price for stock options, assuming the same number of shares.
For an employee, the major down side of choosing restricted stock (assuming non-negligible valuation) is that if the company fails and the stock ends up being worth nothing, you don't get that money back. Whereas with stock options, you have more time to find out if the stock will be worth anything before you buy into it.
The up side is possible tax advantages, but of course I cannot give tax advice.
(All this is information I've learned while being the founder of sandstorm.io; I am not an expert in these things.)
PS. Don't forget to file your 83(b). (Any time you say "restricted stock" to a startup founder, they will instinctively reply with "Don't forget to file your 83(b)".)