There are many tangible and intangibles that go into this question, and there is no correct answer, since the answer, by definition, is subjective to you.
Here are some (but not all) of the things you should consider:
§ What is your company's valuation (and comps)? Since there are multiple ways to compute valuation, you will likely have several answers here.
§ What is the valuation of the acquirer, and the potential value of their stock (to determine your current and future values of Y)?
§ Is your company one in a string of acquisitions?
§ How critical is your company to the acquirer's future value?
§ What is your liquidity for Y, and the acquirer's general liquidity? (Is someone going to buy them soon? Is there an IPO in their near future? Can you reasonably expect to sell your shares if there is no liquidity event and for how much?)
§ How involved do you want to be with the future company? How likely are you to remain there beyond a couple of years (realizing that most principals of purchased companies depart or are ousted within two years or less)?
§ How much money are you willing to leave on the table (read: gamble), and what is the minimum you need to take away right now?
I have been on different ends of this several times and am happy to assist with your considerations.
Blue Cactus Consulting (bluecactusconsulting.com)
There is definitely a better option:
$Y stock = $0 Don't take on anyone else's problems as a minority shareholder.
$X cash = 100 percent of the cash price you are willing take.
In startups, take the money and run. Time is the death of many deals.
This is advice I feel very strongly about, Good luck, D