I have carried and used a cgsj, sjle, sjtac, sjtacle - and I've come to use the choiless boss jack (proto) because it stands out as being better than the rest. the choil isn't as much of a sticking point with others, but these are my reasons:
1:
no choil - this may not seem like a big deal, but I see absolutely no reason to ever lose edge and create a catch point on a blade, I've never felt like I had 'more control' choking up and I am perfectly comfortable grabbing the back of the blade and choking up with it as is.
2:
balance - The choiless version in .220 (proto) has a heavier blade balance than the previous versions, it's comparable to the .250 sjle version but it *seems* more blade heavy because theres more edge in front of your hand, even if it's technically not.
3:
handle - This not an identical handle to the original sj's. The boss jack did the same thing as the boss street, it adressed the core problem with the original third gen handles - the index finger height. On the original 3rd gens the difference between the index finger and the rest of the handle was too drastic, it felt like there wasn't enough meat there, it made it feel like it was a little loose in the hand. This isn't so with the boss jack. You can also get the scales in g10 which I consider a big preference because you can get a grittier finish and it doesn't soak up moisture. I prefer the boss jack's handle to the TAC handles because of issues I've had with the TAC handles. they are mostly a 4 grip handle, in that it's not that comfortable to hold in a back shifted grip since the pommel is a round/spike. The palm and finger swells are also very round and can bite into your hand when you grip hard. Not so with the boss jack handles, which allow a reasonable forward and reverse grip, as well as forward and backward shifted.
Price isn't really an issue here since you already have sj's that you could use. The above reasons make the boss jack a better knife regardless of the price. I consider the boss jack to be one of the flagship 'best of' models that busse combat has ever produced. If I had to pare back to one knife and one knife only from busse, it would be the choiless boss jack I have, because it can do anything, and I can always get cheap slicers or heavy choppers.
I know it seems like it, but the boss jack is not the same knife as the 3rd gen sj's.