I've bought nic from MyFreedomSmokes, Wizard Labs, RTS, and Nude. Honestly, I can't tell the difference between nude/wizard/rts. They are all clear and generally flavorless. MFS is a little peppery. Which I actually like with some of my recipes and the only one I like to vape with no flavor.
Heartland Vapes had liters going for under $50 recently. It's good nic. If I was buying I would go for price vs label from any of the reputable vendors.
If you've bought premix from 15 different vendors, you've already vaped the vast majority of nic bases out there. Unless you can tell the difference between premix nic base, you won't be able to with your DIY stuff. Retail and DIY people all
buy from the same places.