I'm not sure what you expect in terms of answers, but it depends on personal factors. It pretty well has to depend on personal factors, since otherwise everyone would want to do the same thing (either everyone thinks the current price is one to sell at, or everyone thinks it's one to buy at), and there would be no trades. You wouldn't be able to do what you want, except on the liquidity provided by market makers. Once that's hit, the price is shifting quickly, so your calculation will change quickly too.
Purely in terms of maximising expected value taking into account the time value of money, it's all about the same. The market "should" already know everything you know, which means that one time to sell is as good as any other. The current price is generally below the expected acquisition price because there's a chance the deal will fall through and the stock price will plummet.
That's not to say there aren't clever "sure-fire" trading strategies around acquisitions, but they're certain to be based on more than just timing when to sell an existing holding of stock.
If you have information that the market doesn't (and assuming it is legal to do so) then you trade based on that information. If you know something the market doesn't that's going to be good for price, hold. If you know something that will reduce the price, sell now. And "know" can be used in a loose sense, if you have a strong opinion against the market then you might like to invest based on that. Nothing beats being paid for being right.
Finally, bear in mind that expected return is not the same as utility. You have your own investment goals and your own view of risk. If you're more risk-averse than the market then you might prefer to sell now rather than wait for the acquisition. If you're more risk-prone than the market then you might prefer a 90% chance of $1 to 90c. That's fine, hold the stock.
The extreme case of this is that you might have a fixed sum at which you will definitely sell up, put everything into the most secure investments you can find, and retire to the Caribbean. If that's the case then you become totally risk-averse the instant your holding crosses that line. Sell and order cocktails.