What is the best intake manifold for a small block 350?

Intake manifolds are designed to optimize power in a specific rpm range. The best intake manifold is one that optimizes the rpm range you need. If it's a street engine, you probably need one that creates peak torque in a lower range than a race engine. A 2-plane manifold such as the Performer or Performer RPM is good for the street. A single-plane such as the Victor Jr. works better on the race track.