I suppose it depends a) which brand you did your original beauty therapy training in (some may train in dermalogica, others in decleor ect ect) and b) your budget. Are you working mobile or in a salon? How big is your current client base and what do your local competitors use? what are you using at the moment? It's nice to choose a brand on the basis not only of preference, but also to find a niche in your local market place.
I use Priadara, as it's friendly to my budget (which is minimal), it uses natural ingredients with bio-friendly packaging, and it's a niche market as no salons in my local area uses this brand to my knowledge.