yeah... sannies jack herer is one of the top jacks out there from everything i've read.
as to sativa seeds' jock horror (nirvana's moved all of their sativa dominants except pure power plant to their sativa seeds line, maybe that's why you're confused), it may or may not have some skunk #1 in it. there used to be unconfirmed rumors and heated debate about skunk #1 in nirvana gear. their stuff is generally considered pretty good though, especially for the price as long as you don't get their fems & autos, but not as refined as stuff like sannies' or TGA subcool's gear as they work their strains over with that extra attention to detail.
if you're out for some jack, check out TGA's jack the ripper or jack's cleaner 2. those should be great too.
i still haven't tried ANY jack herer yet (never liked the reports i read that say it can get a little skunky & stoney) but i can say i really love high quality seeds' haze x skunk. it's the trippiest indoor i've smoked so far. i'd say it's got to be at leastr as good as jack or better, especially seeing it takes 12 weeks to finish where jack's are faster.
i THINK sensi seeds might be another good source for jack herer too. i've seen at least one person repping that, but that's all of the sensi seeds feedback i've seen so far.
sannies is the safest bet & not expensive either. i'll probably try it myself if i find i do like some of the jack crosses i'll be trying soon like autoflowering cinnamon girl & jacks cleaner 2.