[bobcowan]

It depends on the application.

The air:fuel mixture needs to be moving along towards the cylinder fast enough to keep the fuel in suspension. If it slows down too much, the fuel will drop out of suspension and puddle up in the manifold, and the engine will run lean.

With a big cam, big heads, and big intake track, that happens at normal idle speeds. That's why you see high performance carb engines idling at 1200 rpm.

If you're building an engine like that, then I would recommend a port injection. It helps to avoid most of those problems, and it will idle pretty nicely at low rpms, and be very easy to drive.

Also, the port injection system can time the injectors to fire at exactly the right moment, just as the intake valve is opening. That makes more power with lower emissions, and be more efficient.

If it's a fairly mild engine - stock cam and heads - then the intake charge will be moving along pretty quickly at low speed. And then a TBI system will work fine.