Vigen is a herb that is popularly used in Cooking for many good dishes for melee and casters. Vigen can be found all over the place in southern Beluslan and far northern Brusthodin. It is very easy to farm and still sells quite well on the AH for how easy it is to get. The best place to farm for Vigen is more of an opinion then anything.
Depending on what you're looking for while farming it will determine the best possible place to farm it. If you're looking for the safest place then BuBu Village is your best bet. You can find about 3 spawns inside the town here. If you're looking for the best possible place to get it I'd say east of Red Mane Cavern gets my pick.
I know a few people that farm just north of BuBu Village which is a good place all fine an dandy. The only thing I don't like about this place is it's unsafe if you're not level 47 or higher also since the mobs here are so high level they will agro you more then the level 42's in Beluslan. But as said before, where you want to farm it is entirely up to you.
Vigen in Beluslan
Vigen in Brusthonin