I can't comment on any of the companies mentioned and wouldn't want to be unfair to them - but you do get what you pay for. Good quality essential oils are NOT cheap.
Personally I think you can't go wrong if you stick with the ATC approved suppliers. The ATC work very hard to keep high standards in aromatherapy and their members pay to join. They wouldn't do that if they didn't think it worthwhile.
The suppliers mentioned may very well be excellent and I really am not knocking them or any therapist who uses them - but consistency of some sort is important and if you get good results with an oil then you would stick with the same supplier wouldn't you? I use Absolute Aromas and Fragrant Earth - they are expensive - but then I don't have to worry about the oils at all - I know that they are fantastic and they won't let me down. Not only that but you use less of the oil. One drop of Rose Otto is more than enough in a full body massage and I only use two to three drops of any of the others unless it is Peppermint or something to numb muscle pain. I can use a lot of that - in fact I use it neat - because I don't have to even think about the quality of the oil and any side effects.
This is from the ATC website.
* The Importance of Purity
High quality essential oils at a cheap price are simply not possible. As with most things in life, when buying essential oils you get what you pay for. To achieve optimum therapeutic results in aromatherapy and influence health, essential oils need to be of the highest quality – pure, unadulterated and natural - and not altered in any way since leaving the still. Poor quality products simply do not work and they may lead to skin irritations and side effects as is often the case with synthetic drugs. The whole oil contains many chemical components, some of which are present in very small quantities that cannot be identified and are known as trace elements. It is thought that these act as "quenchers," preventing possible side effects. So with this in mind you should always endeavour to purchase your essential oils from an established, reputable supplier who has been in business for many years and who is a member of a recognised trade association.