I'm piecing together my dream custom guitar, so, what type of neck build is best in terms of sustain/tone. Is neck-thru still the best? How does all-access neck joint work, and is it better than a neck-thru?

And how are Carvin necks? Better/worse than an Ibanez? Enough to make someone want to buy an Ibanez over a custom Carvin?
Neck Thru will ultimately hands down have the best neck access. but i wouldnt go as far as saying their the best as theyre not great if you happen to snap your neck in half. and how does aanj works well think of a fender strat bolt on heel block. now shave half of the wood of that so ultimately when you slide up in theory you should be able to reach further up the neck compared to the original when you had a huge block very much limiting your progress