Trek 6000 for a beginner
Trek makes good, reliable bikes across their price range.  I have 25 of 'em in our patrol-bike "fleet" at present.
The 6000 is well-reviewed, but it is designed and delivered as an off-road machine.  It will be less than optimum when ridden on pavement.
If you were going to spend most of your time riding on pavement, then a simple change of tires would be of considerable benefit.
Not that you can't ride a mountain bike on the road, thousands do so all the time.  It's just that those knobby tires will squirm and wear rapidly, and the riding position is not the best for long stretches on the road.