The Shivans and GTVA are very different, and the Shivan thrusters have always been a bit naff. I like the taylor 'red trail' because it blends well with the thrusterglow. As VA shows, the thrusterglows don't look very good without a thrustercone thingy, and the Shivan thrusterglow is often far too large for the thruster, so it looks like a huge disk attached to the ass of a ship.
MetalDestroyer - the 3d cones are strange, and they don't seem to blend properly into the AB thrusterglow (as you can see in those pics). My problem with the 3d cones is that they look rubbish, not the idea of 3d cones, and since the 3d ones actually fade as they trail (woo textures) instead of the inflatable look for taylors it's arguable how much of 'the look' is the effect and how much is the art used. Either variant could be fine, but thrusters have always looked more-or-less rubbish in FS, and I think we need to sit down and decide how we want them to look and what the best way to get that look is. Also, taylors 'glowcones' look MUCH better on capships than the 3d cones, as the 3d cones are far too short (barely visible) and so capships just get stuck with the thrusterglows. This is a significant problem with Shivan caps, as their thrusterglow looks awful.
Also, teal AB = the lose. That's something I'm prepared to just come right out and say. AB should look awesome and aggressive, not soothing and relaxing.
EDIT - For what it's worth, huge thrusterglows and long thrustercones aren't prominent in cutscenes etc. It's arguable, then, that they aren't very 'Freespace', and that smaller glows and shorter cones are the order of the day.