I've owned nearly all of these except the J-3, and my favorite is the 61LD because it''s close to a Leica in IQ. Probably not the same in resolution power, but what do you expect for 1/10 the price. The Industar 22 would be a close second, but by it's very nature isn't as user friendly.
Like all things FSU, your sample may vary....A LOT! If you're lucky, it will at least focus. I've owned more than a few that had been taken apart and put back together in a "less than optimal manner". Don't expect great build quality w/ the 61LD, but at least it has click stops, nice coatings, and a wonderful way of making images. The J-8 is sharper and of better construction (at least the later black ones are), but that sharpness comes at the expense of some character, for lack of a better word. If you shoot Leica vs Zeiss, then you know what I mean. Best bang for the buck, buy an 61LD w/ any variety of FSU body/lens cap and have a ball.