I've been buying all my Li-ion cells from the Orbtronic site. They are in Florida and sell Panasonic and Samsung cells. The site has an "Amazon Pay" option so that makes it easy too. (if you have an Amazon account anyway)
They might be a few bucks more per cell, but I've been happy with the quality. The contacts on the cells seem to stay cleaner than other cells I've had.
Depends on what I need, but much of what I buy (Li-ion) comes from 'batteryjunction', as well as primaries, NiMH, and a fair number of flashlights, etc., etc. They're a seriously good operator. Many, many orders over nearly a decade, never one mistake, and very good Cust. Svc. I believe they're a DBA of Shore Power, Inc. (wholesale distributor), which means little to me except that they apparently have a serious organization behind them. For something BJ didn't carry, ILLUMN also did well for me on an order or two. No single distributor carries everything, so it's good to have a couple one can count on. I also get K2 LFPs from 'batteriesinaflash', as not everyone handles that line, and they've done fine with those few orders.