$500,000 now or $10,000 a month for the rest of your life [tax free]

10k a month, definitely. While I'm not a hundred percent certain I'll live long enough to get more than the 50k lump sum, I am pretty sure that getting drip-fed the money would assuage any fears about paying bills, and help avoid the temptation to splurge it all on inane bullshit.