Given a choice between United and Singapore Airlines (or any foreign carrier for that matter; yes, EVEN AIR CANADA), I'd pick Singapore Airlines every time. But I can't sleep on planes anyways so inability to sleep doesn't make any difference. And at $7k, they'd better be waiting on me hand and foot.
If I'm spending $7,000, I'd be spending it on Singapore Airlines, period. As far as entertainment goes, I'll bring a laptop and some Boston Legal DVDs to kill time. As far as seats go, I can't sleep on planes (or anything that moves for that matter) anyway. And United's 747's are disgusting and not fit for human occupancy for any period of time, let alone for 11+ hours.
But caveat emptor because I'm the one that secretly wants United to go belly up.
But seriously. It comes down to value for the money. Singapore Airlines has a highly publicized reputation for excellent service and being far, far ahead of the curve when it comes to product and service. SIA built an entire company on it. United generally gets an F in service from many people. And if I'm spending $7k-$12k on a plane ticket, whether it be my money or my employer's money or my parents' money, the level of service you'd receive on board a Singapore Airlines plane is the BARE MINIMUM. You can tell me that my standards are too high, I don't care. It doesn't change the fact that quality is critical in my decisionmaking when it comes to spending $12k. I'd book with Singapore Airlines in a heartbeat for the same reason you couldn't pay me to buy, or drive for that matter, an American car.
When you're dropping $8k on a business class ticket, decent, adequate, very nice, good, whatever, isn't good enough. What I get better be, at a minimum, excellent. In other words, I won't be satisfied until I'm blown away by the sheer excellence of the service. The planes better be spotless. The service better rival Ritz-Carlton. The food better be comparable to a Michelin 3 star establishment. The product itself better be one of the best. UA loses in 2 out of 3 categories.
Actually if they truly value my business or hope to see me again on some future flight like they say at the end of every flight, they'd be exceeding my expectations every time. A problem-free flight is the minimum. Every little problem, no matter how insignificant, is a strike against the company in my book.