The important traits to look for are the ones that you care about the most.....everyone is different. I always look for early finish and heavy resin production.
that's why it's called selective breeding... you pick the traits you want.
i always used to select the shortest flowering male to lower flowering times, but DJ shorts or subcool suggest the opposite, selecting a non-dominant male as recessive traits are where all the interesting flavors and buzzes come from. especially with hybrids, the afghani will want to dominate.
as you'll already be testing you females, at least, you should know which ones have the traits you like best. if you REALLY want to get serious though, test your males too. that's the only way to know what each brings to the mix. it's your grow, you're in charge, you get to decide what the ultimate plant is. tastes vary. if you look at the gear everyone grows, no two growers select the same strains. only you know what floats your boat. with ANY strain out there, there's someone who loves it, and someone else who hates it. your offspring should be a reflection of your tastes.
i'd suggest that instead of concentrating on brute force productivity and resin content, you look instead for QUALITY... a better buzz with more than one THC trait. (i'm hinting at how much i hate 1 dimensional stones... but that's me) select for flavors too. asfar as i'm concerned, a better tasting strain with a superior high is worth a little extra wait and a little lower yield. when a breeder selects for quality over quantity, people will recognize it when they smoke it.
