It depends. Is the carpet glued down or does it have a pad behind it?
If the carpet has a pad behind it, you can't beat a modern Sanitaire with a VGII brushroll installed. They've got the airflow and the vibration to get the dirt and grit loose. Nothing will clean a high traffic carpet like the combination of airflow and agitation. An older Hoover with the beater bar agitator will work well too, although I'm assuming you're wanting a daily-driver, hence the Sanitaire suggestion. A good sweeper won't help you here. Agitation is essential to get the "crud" out of the backing of the carpet.
Unfortunately if the carpet is glued down, you'll need a good sweeping action since vibration will do nothing for you there. In the glued-down case, pretty much anything that sweeps will do about the same job since airflow can't get behind the carpet to clean from below. At my work we actually use an older plastic-based Hoover Convertible with a Cleveland Wood Products 4-row brushroll. It sweeps well and has just enough airflow to clean the glued carpet, but not so much suction that it seals to the floor.