I find the Eqyss detangler is the best. A friend got an OTTB who was left to pasture and had a tail full of burrs and knots. Most poeple would have shaved it off. We stood there for over an hour working on it with the detangler and it came out very easy and we managed to barely pull out any hair in the process.
I also acquired a Wb gelding who was on pasture for 3 years and his tail was full of burrs and tangles and it was extremely thick. I did the same and had the exact results. Remember too, don't use a comb if possible. Just finger comb until everything is out and then use a wide tooth comb to get any small tangles out =)
I have a lot of friends who use Ecolicious products with GREAT results. They are all natural, 100% biodegradable and earth friendly. Its a local company (made in MB, Canada) and I actually know most of their models on their site. I heard their detangler is amazing too! My friend actually uses it on her own hair! I havent used any of their products on my horses personally but after Im finished with my two bottles of eqyss detangler I plan to try theirs =)
DE-STRESS Intensive Restructuring & Detangling Treatment  - $23.95 : EcoLicious Equestrian, Natural Horse Grooming Products