i prefer an earlier harvest with less cba or whatever the fuck the smoky->coloration process is showing THC breaking down into whatever...
personal preference will make a bit difference between 1 person and the next, so always take this type of advice and translate to your preferences... if you don't know your preference, don't assume it... try early / middle / late and you can decide whether a few extra grams is worth the wait or if you want high percentage of amber, regardless etc etc..
density of nugs
pistil coloration
trichome degradation (smokey is the start of degradation, despite common belief otherwise)
supposedly, the more amber the more of a sleepy / couch-lock effect you get. i don't like falling asleep after smoking a big ol' joint... i harvest early. colas must be dense, >50% pistil coloration/retraction / hint of amber in any location.. not just isolated. thats what i like... these 3 observable traits keep me consistent... cause trichomes may be the best option, but they are not perfect.
new growth and some oddball plants will deceive your eyes as far as the coloration... heard of some 'sativa' trait where they don't turn amber at all or the plant is rotting by the time it does. it's good to have a baseline for more than 1 observable trait to guide you... even if you mostly rely on 1.