The NES original is a classic, I remember spending many a time playing through it on a friend's NES. The Speccy and Amstrad ports aren't *that* bad, but really let down by the lack of directional fighting moves. They are at least quite pretty though, with some nice parallax effects. It has to be said that emulators don't really do the Speccy version justice, as without the PAL colour bleed and pixels that are too sharp, they tend to highlight the blockiness of the graphics that you didn't really get on the real machine. The biggest problem with the game is that it was laughably easy, once you get the hang of switching turtles at the right point to avoid any of them losing too much health and using pizzas effectively.
The Amiga version though, wow that looks really, really bad. I don't think I've ever seen it before, but you'd be gutted if you forked out for that and then saw the 8-bit versions.