I think SQ beats UA hands down in terms of service and overall experience in C-class. However, what always impresses me about SQ is during situations when they are asked to go above and beyond their normal job duties.

Example: Since my wife and I came from two destinations, we booked our last minute SQ flight as two seperate itins, therefore receiving two different seat assignments. During check-in on the return flight, we expressed our desire to sit together on the flight, if able. The flight being completely full made it more challenging so I did not have my hopes too high on it. The RA said to mention my request to the people at the gate... she also made a note of it on my account. When I got to the gate, and before I even re-stated my request, there was a gentleman (a passenger) standing next to the gate inquiring about my name and seat number. As it turned out, one of the SQ agents made an announcement and asked this passenger to switch seats with my wife's original seat (way back of the plane) to fulfill my request. In return, SQ offered him something free (a deck of cards? hehe). The gentleman was totally cool with it. Pretty amazing that they did this considering my wife and I have no status with SQ.

I have a couple of more examples but I think this paints the picture.