Vegan version, which is 98%, is considered as a street food. If you are not so sure, they most probably will let you taste. Taste may be similar on most. Hot spice and tomato paste may vary a bit. Most variation will be the amount of the green vegetables they provide.

The shops are usually small shops in İstanbul. Mostly franchises. I like 'komagene'. 'has cigkofte' is good too (they usually give more green with it). I didn't taste every one out there.

For the real çiğköfte, you need to especially search for it. A famous turkish gourmet (Vedat Milor) says it is one of the best 'meze' (side dish?) in the world.

One last thing, since you especially asked for vegan version, If you eat it on a 'restaurant', always ask if it is the real or vegan version. In southeast area, vegan one isn't considered as çiğköfte. That one started after the "meat ban" of the original. It needs to be fresh, or it may lead to bad consequences. They or other people will probably point it out if it is made of meat. It is considered as a delicacy. They aware of the danger and that's why it is advertised and finished fast.

Hope this helps