Jackson necks for me :)
Either of their main profiles - the "Tranditional Charvel" (I think they call it the "Standard" these days) or the "Speed Neck" - are equally good for me. There's not a huge amount of difference in thickness, both have that really comfortable flat-backed "U" shape, a 12-16 compound radius, flawless finish & fretwork, with nice tall (usually 6000) frets.
I like the PRS Wide/Thin, Gibson 60s (when the frets haven't been installed blindfolded :roll:), Warmoth Std Thin amongst others, but Jackson necks feel to me a cut above everyone else's.
Don't like Ibanez - the straight 16" (& sometimes 17") radius is too flat for comfortable chording & arpeggios on the lower frets. JMO, YMMV etc...