Twilight Highlands is my personal choice for my gatherer with maxed mining/herbing. Be sure you're checking the path around Grim Batol for both ore and herbs.
Associate Professor Emeralde ~ fire-starter, flower-picker, potion-brewer, and artifact-finder
It depends on what kind of herbs/ore you'd like to get. Twilight Highland and Vashj'ir are my favorite places. There are a lot of Elementium and Pyrite nodes there, and also a sufficient amount of Twilight Jasmine in Twilight Highlands, while Vashj'ir is the best place to farm Azhsara's Veil.
Twilight Highlands in my opinion, if you're not a low level that's going to get ganked by the mobs too easily. If you are farming at low levels (which I was for a while hence me mentioning it), ie. 75-80 then you may struggle with the mobs and Uldum has a pretty simple route and almost no mobs that will attack you - however Uldum also has no mailbox which can be a bit of a pain!
I often find a higher amount of elementium in Uldum if I'm alone there but it's a short route so can feel heavily populated with just 1-2 more people farming - it does however have hefty amounts of herbs along the river banks (well guarded by crocolisks though which slows you down).
The Twilight Jasmine makes the TH route worth it really due to the high price and demand this usually commends for inscription, and as TH has a lot larger route it can accomodate a greater number of farmers so it doesn't feel too crowded. If you're not finding any herbs you may want to change your route slightly, I usually get around 80-100 Jasmine per 200 Elementium following a mining route not a herbing route.
So overall I'd say TH unless you are getting whacked by mobs in which case I'd go with Uldum as the safest spot.