What you describe is what I call a 'stumble'. The MAF is the most likely culprit, followed by the fuel pressure regulator & pump. When you step on the gas pedal, the throttle opens, and the gas, air, can flow right in. It will flow quicker, or accelerate into the manifold, quicker than liguid fuel. To make up for the blurt of air, the fuel pressure regulator bumps the fuel pressure to allow a richer 'squirt' of fuel for that short period of time. If the MAF lies or the regulator {pump, filter, possibly} aren't quite there, you'll get a stumble, just for a short time until all the other stuff 'settles down' to a more or less constant flow. At least that's how I understand what's happening.
tom