Another Glow Plug CLip Question

From what I can find there are basically 3 glow plug clips available. The standard Cox clip of which there are probably a million or so of them out there, one made by Sullivan, a yellow model and a different one sold by Cox themselves. Of these clips which is going to give the most constant contact with the plug ensuring a reliable light. Preferably out of the box, absent having to ad d wires to the Sullivan one.
I ask because I am currently using a standard Cox clip with heavier wiring soldered on 3 inches from the clip but I can tell it is not always making good contact. Really frustrating when yo are flipping a probp with a glow plug that is not lit.