I don't think I have any "universal" rules aside from not liking short headstocks, like the Ernie Ball ones. They just look stubby to me. I also tend not to prefer anything other than a six-on-a-side headstock on Strats/Strat-like objects, or really on any similarly asymmetrical guitar design. 3x3's are fine on Les Pauls, SG's, 335's and the like. Other than that, my dislikes are more specific. I don't like the look of Epiphone headstocks on LP's and SG's (they're fine on other designs). I really don't like these kinds of Firebirds (I can never remember if this is reverse or non-reverse): Finally, I feel if you're going to copy a classic guitar design, just copy it all the way. For instance, I'm not crazy about the Silver Sky (basically a Strat south of the neck heel) with the PRS bird inlays and headstock. But a Silver Sky made to be less obviously Stratty could be just fine by me.