I've got the straight stitch and the zig-zag machine, the 4-thread overlock, the free arm machine, plus an extra for buttonholes (built-in buttonhole drive -- really slick and a pleasure to use).
I'd need the industrial zig-zag and the 5-thread.
The reason I specify a zig-zag industrial is purely for versatility. Some of the zig-zag industrials I've seen produce as good a straight stitch as any.
I wish one machine could do it all.