So far I've used:
Blu: Good luck getting anything from them in a realistic time. Never tried the product as it took a month to show and I unloaded the kits as fast as I could while they were still in shrink wrap. (waiting on these in frustration is what led me to ECF in the first place and my first 510 orders)
Volcano: comparable to Blus meaning not the greatest vapor producer but supermini size. Seem to fit the bill for some light ex-smokers and they suffer none of Blu's horrendous turnaround times. I never tried their high end PVs.
LibertyFlights: One of the best hardware suppliers price wise. Many here swear by them. Waiting on my Riva kits to decide beyond price but CS is very responsive even on a sunday!
Altsmoke: Nothing really stands out except stupidly fast shipping. 4 days=acceptable, 3 days=great, they got my order to me in 2. Decent prices but wish they had a deeper selection. Good choice for emergency supplies.
GourmetVapor: My current choice for liquid. Absolute control over your flavors, mixes, vg/pg ratio. AFAIK they've still got a 40% off sale rocking right now. Use code GV40.
