Well, unless if the 20 year payment option (pretty sure it's over 20 years, right?) gets the payment below about $500k, you'll be losing half of anyhow to taxes. Ok, so that's half instead of quarter.
But if you take the hit up front, taking a quarter, then drop that lump sum into a diversified portfolio... if you didn't touch it, I'm guessing in 15 years you'd have doubled your money, thus equaling the 20 year payment. Average S&P, minus 15% capital gains, overall growth of 5-6%? Of course, if you play the market, or maybe sink it into rental units / real estate, maybe you'll double your net worth long before 15 years.
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Pretty sure no amount of money will make relatives go away. If they aren't good with money now, they certainly won't be if they know you're getting a check every (month? quarter? year?), a huge check. Another reason to take it lump sum: those who aren't financially savvy won't realize what you're making in investments, especially if you don't tell them. Just tell 'em you spent it on hookers and blow, and that's why you kept your day job.