Yeah, seems like a straightforward choice.
> Paying the bonus.
Gimme, gimme!
> Improving office amenities.
Not bad, but... it would depend on how much money we are talking about, and what office amenities it would buy. For example, once I got a new $1000 office chair that felt less comfortable than the old cheap one -- I definitely would have preferred the cash. On the other hand, once I had to work with a barely functional mouse, and I would gladly spend my own $5 to buy a new one, but that would be against the company policy, so I couldn't.
In general, greater computer screens, more memory, more disk, better mouse -- good idea. (I have no idea what makes many software companies try to save money on this. It is a fraction of the developer's salary, and it can have huge impact on productivity.) Expensive chair, expensive table, art or whatever -- I would probably prefer its worth in cash, because companies typically buy stuff way more expensive than I would. Fit ball could be fun, though.
At the end of the day, the cash remains mine, especially if I invest it wisely. The office amenities that company gives, the company can take away. And I can't bring them to my next job either.
> Buying each employee an expensive present.
Just no. If it's something I want, I can buy it myself. If you buy it without asking me, there is 99% chance it has zero value for me.
> Funding a family vacation for each employee.
Again, I can do this myself, if you give me money. And I prefer to keep my family separated from my job, thank you.
> Making a sizable donation to a worthy cause (collectively or for each employee).
Another thing I can do myself, thank you. Also, high chance the "worthy cause" will be something super politically correct, and I don't want to be that bad guy who publicly opposes it.