Twilight Jasmine is the herb that I have the most problem farming. It doesn't matter what time I am in the zone (mostly it is in off-peak hours, often 01:00 - 03:00) and I have trouble getting two stacks within a 30 min period.
Contrast this with Tol Barad Peninsula when I can gather four stacks of Azshara's Veil within 15 mins during off-peak hours.
yeah, let's live in the past! man i loved BC. why can't herbs spawn like they did back in hellfire? oh oh oh, great idea here! let's add a 30% buff to raids so everyone can kill Nef three months into a brand new expansion too! i love easy mode. Blizz, HELP! (cough)
twilight jasmine is a pain, whiptail was always much easier to farm. the phasing is one problem but so is the availability. i get excited when i find 2 nodes after doing a circuit on the western side - it counts as a good day. or maybe its just more people are doing alchemy since flasks are that much more important, the vial, and the awesome trinkets it offers. scribes dont care and will use whiptail to get their crap.