In order of preference:
1) Road bike
2) hybrid
3) hard tail mountain bike with slicks.
I own a Ti MTB with slicks & use it to commute to work (pot holes would destroy a road bike). I've done 50 miles in a day, but I know a road bike is designed for it. The only problem would be price if you don't have a bike. Besides, if you don't have a bike, are you in shape to do 50 miles?
In order of price:
1) Hybrid
2) quality (light) hard tail MTB with slicks
3) quality road bike