In most instances, the stock is restricted for the employee.
If you have a choice between the two, it helps to know what those differences are.
Grants with conditions are referred to as "restricted." Grants become unrestricted, or "vested," when you have met all conditions and are free to do whatever you want with the stock -- such as sell it.
The tax treatment of stock grants is fairly straightforward.
When you sell the stock, the difference between the sale price and the share price when you exercised the option is treated as a capital gain.
Using stock rather than cash to compensate, reward or motivate people is attractive to companies that don't want to part with cash -- especially startups, which may have weak cash flow as they get off the ground.
With nonstatutory options, you incur no tax when you receive the option.