I currently use a Blackrapid Classic Sling.
Would like to carry a holy trinity of lens (eg 3 x primes) or 2 x primes + 1 larger zoom (24-105 or up to a 70-200 if possible).
Would really like it to be as small as possible and to be secured to my body. Convenience is more important than size, so i would go for something smaller if it meant i could access my stuff more easily.
Ability to carry a small tripod would be a plus, but not essential.