I've used both Wiz Labs and Ecigexpress nicotine, and both seem fine. I will say this, though: Ecigexpress's packaging leaves a GREAT deal to be desired; it was a simple childproof bottle enclosed in a ziplock bag, and when I got it, the inside of the ziplock was extremely wet with what appeared to be the contents of the bottle... which was 100mg nicotine, so I had to open the bag and clean up the mess with gloves on, before I could do ANYTHING with re-bottling the nicotine into glass bottles. So I probably won't buy from them again, and will go back to Wiz Labs, which enclosed the bottle in 3 ziplock bags, and none of them was wet with anything on the inside. The only real downside to ordering from Wiz Labs is that they're in FL, and FL's postal service is a joke; one state line away from me, and it takes 1-2 wks to get ANYTHING from anywhere in that state.
Andria