Depends on what you want. Some dexters are more dairy type but others have a pretty good beef conformation.
http://www.legendrockranch.com
How much land do you have?
Do you intend to keep it a hobby or side line?
They may not bring top price at the sale barns but cattle are a crap shoot anyway regardless of the breeds
If you are mostly interested in raising food for your family and selling an ocassional freezer beef Dexters might not be a bad choice. They have a good reputation for meat quality if not quantity.
If you just want something to help keep the grass and weeds down they will work as good as any.
MOST IMPORTANTLY. Are you primarily interested in pleasing yourself or impressing others?
I raise 'small' cattle.
My 'advantages...'
They tend to be gentle and calm
They are easy to handle especially if you have to work them alone. I remember the first time I got stepped on. Sure was glad the ground was wet and soft and she was'nt 'full sized'.
They fit in the freezer without having to find buyers for the excess
They are easy on fences and equipment
As you get older these are all important considerations.