I have both and use both of them. Each has it's uses that it is best suited for as described by the others. Besides woodworking projects, I have used my Jig Saw for cutting and filing metal. Most recent was making a replacement electrical cover plate for an A. O. Smith 3/4 HP Motor. Previously I made a replacement Splitter for the Blade Guard on my Model 10E S/N 1077 restoration. I could not simply buy a used one for it since the very early splitters had a narrower strip between the knife edge and the slot. See a picture of it on the Jig Saw table below, it is the one on the left. I was able to do some of the cutting for both of these projects as well as filing on the Jig Saw. I have quite a few of the files for the Jig Saw. Another thing it can be used for.
As for getting replacement parts, you are correct, it is getting harder to find them. If you need a replacement gasket you can make one. We talked about that in a previous post. I am not sure if any parts are still available from Shopsmith but you can search for them by the part number to find out. You will need a later parts list with the six digit numbers most starting with 5 and not the numbers in the manual from the 50's if you have one of those. Parts do come available at online auctions from time to time. The only change to the Jig Saw from it's introduction in 1954 until it was discontinued was a change in the table tilt lock for which you can buy the parts locally. It was a change to an Allen Wrench Cap Screw and Washer from the original Trunnion Bolt Assembly of the Knob, Threaded Stud and Washer.
Shown in the picture above is a splitter for the very early 10E (version 1) on the left and the later 10ER (version 3) splitter on the right being made. I had a later Upper Blade Guard without a splitter so I was making one for it too.
Mark V 520 S/N 09-11-01 completely upgraded to Mark 7, with all SPT's & more.
Model 10ER S/N R64000 first one I restored on bench w/ Shopsmith metal ends & retractable casters. Has Speed Changer, Model 4E Jointer, Jig Saw with lamp, a complete set of original accessories & much more.
Model 10E S/N 1077 oldest one I have restored. On bench w/ Shopsmith metal ends & retractable casters.