I'm not sure I have an ultimate must have machine. There are more than a few on the "want" list. I still want a few examples of earlier electric conversions for my "History of Electric Sewing Machines" display and there are a few older machines that I just plain like the looks of. The Free art nouvaeu Peacock machine is one and the Franklin Scarab pattern machine is another. I like anything with MOP too.
White had some really funky Art Deco designs that I really like as well under their own name and as some of their badged machines.
A patcher would be nice too though I doubt I would use it much.
Rodney