For me, the thing about swaps is there's a deadline and a commitment to other people to keep your word when you have said you will participate. The thing with sew-a-longs is other things can happen to draw my interest, change my mind, or change my schedule, then I can put off keeping up with it. I can see that no deadline can be a positive, but for me it tends to be a UFO. But I prefer the sew-a-long because of the things mentioned: use your own colors, sew seams your own way, no postage. I also like them because of less stress-- I sew to please myself and don't need to worry my sewing doesn't please the person who receives it.
Burgoyne Surrounded is on my to-do list.