I've used Veniard, Fulling Mill and Franc N Snaelda bucktail. Primarily for saltwater patterns. For clousers, deceivers and similar flies the Franc N Snaelda bucktail is the best for consistency, length and value. I've had good experiences with Veniard but the consistency isn't always there and the Fulling Mill premium bucktails are more expensive but in my experience not as good.
The Franc N Snaelda tails are always a good size, with long fibres and reliable quality.