Those Pacesetters make everyone jealous!
My favorite is my 1916 Singer 31-15 treadle, AKA "The Tailor's Machine." It has a 16" flywheel which gives excellent control and goes like the wind on the straightaway. No features - nothing but forward stitches; tacking means you have to turn your work around or hold back to make several stitches in one spot. Utterly reliable and forgiving. Will go through several layers of canvas or fine silk without complaint. Domestic machines feel cramped by comparison.
To complete my "collection" (accumulation is probably a better word in my case) I'd like a Pfaff 138 because it has zigzag and reverse.