I agree with snappy llama on most everything. I find that some of the on line suppliers are actually cheaper than local sources, eg. the Snappy coconut oil, which works fine, is cheaper than Costco and got delivered to my door via Amazon Prime the very next day (love Prime.) On the other hand, some supplies are much cheaper close to home, I ordered tallow from Soaper's Choice - great source and relativelyl inexpensive - before I read posts about buying it at Smart and Final in 50 lb boxes for @$32, an unbeatable price.
General supplies: in order, I usually order basics (oils/butters/lye/additives) from Nature's Garden, WSP and Brambleberry. NG seems to deliver the best combo of customer service, speed of delivery and value. Brambleberry is fast and has great customer service but is a titch more spendy and I have experienced problems with packaging (spills/tears in almost every order.) WSP has a great range of products but has a $40 minimum (I just keep a running total in my cart an checkout when I get to that amount), also they are by far the slowest in shipping.
I don't find there is much of a difference in the quality of this basic stuff, some of it comes down to what you prefer to use. Eg, I like the lye beads from NG because the lye flakes from BB tend to get powderized and make me cough when I pour them once I get to the bottom of the bottle. Other folks prefer the flakes because they are easier to measure and have less static, it just depends on what you want.
FOs are way harder to recommend, I have favorites from about 10 places after testing hundreds of them. I think this is just a long journey that you have to undertake yourself depending on what you like. An invaluable resource in this respect is the Soap Scent Review Board, which concentrates on offering in-use reviews of FOs and EOs. This board is so awesome because there is a huge amount of information on how FOs react w/r/t acceleration/discoloration/ricing, etc. There are a few scents that I love but use only in BB/mp based on SSRB reviews, I like to swirl in CP so tend to use only FOs that I know will behave well, SSRB is hugely helpful in finding out that information.
Edited to add: If you join SSRB, please post as much as you can, it only works b/c folks are so good about doing that. I admit, I posted a bunch of reviews when I was only doing MP and am a bit embarrassed about them now, I suspect they were not that helpful and potentially a bit irritating to the mavens. But the posters here are so helpful, if you can join in, do. As Lilli, the board owner says, it is a "pay it forward site."