Is price not an issue?, I am doing EWR-SIN 3 or 4 times a year at present and since making MM I always check SQ and Emirates, but generally find the price premium to large to justify taking them. I have yet to fly Emirates, but want to, but if price, times and miles were not a consideration I would pick SQ every time.
From SFO (and LAX) UA and SQ generally match fares. In fact, it's been SQ setting the fare and UA matching recently. There's basically a war west coast to SIN right now.