I put mine roughly on the upper half of the curve of the neck, like I was pinching with my thumb and middle fingers, when chording my hand slips to the c style position, but like Jimi I am using my thumb to mute the e string half the time.
I was taught by classical teachers my first years learning guitar, so that is why I got the thumb thing correct, It actually allows more of the fingers in front of the fretboard and speeds up your playing, plus gets rid of those cramps.
when chording, if you do the typical barre chords then you will keep the thumb on the neck, but once you advance past the barre chords and start to use inversions then you will start needing to grip it a bit different to get some of the reach. Barre chords are great way to learn chords besides open chords, but to many people stop with the e and a forms, those are just the beginning ones. Most chords I play do not use the low E or the A string, I figure I have a bass player to hit those so I like inversions built of the F, D, and higher A forms.