The first electric guitar I had a chance to play was a MIM strat with what fender call the "modern c" shape. because of that, I can say that the fender of my generation (I'm 25..) modern C is the shape by which I judge all others (just psychological, I suppose, being that my first impression is based on my first experience..) I never took issue with the "modern c," and have owned/played many with the same profile since..
Then came my intro to the LP-specifically the "fat '50's" profile- and I have been in love with thicker necks, with a nice V - or U shape(much like what is on my Korina McCarty-Brazilian with Wide-Fat neck carve..). Since, Gibson has come out with a newer asymmetrical design, that to me at least, feels like a Taylor Acoustic--and as for a LP, just doesn't do it for me.
As for tone, I'm not sure.. I feel like the way the neck is connected to the body, and the wood that the neck is made of offer more to alter/improve the tone more than the shape. You always read that a bolt on neck inherently has less sustain than a glued in neck. I can't say for sure I've experienced this, as my time with bolt on necks doesn't stack up to my time with glued in necks.
As a side node: I'm only 5'7" and have what most would call small to normal sized hands (not Burger King commercial territory..), and if I'm playing a guitar with a thin neck for any long period of time (2+hours) my hands do cramp up. However, with a wider, fatter neck, I don't seem to have that issue.
wide necks for me.