title_body: Ground coffee or beans
upvoted_answer: Ground beans have a much larger surface area by weight than whole beans. When the surface of the bean is exposed to air chemical reactions take place. I doubt that these reactions have been completely characterized but at a minimum they include some loss of aromatic oils. In other words, the processes that lead to a judgment that coffee is "old" happen faster in ground coffee.  
  
  You can do the experiment easily and cheaply by comparing the results of coffee made with freshly-ground and pre-ground versions of same brand/date coffee. You can always borrow a grinder.
  
  The experiment might not work if both samples of coffee are old (or poor quality). Otherwise I think you would notice a difference. Whether the difference is worth paying for is a different question; but the only costs are a grinder and time to grind the beans. 
  
  A short answer to the question about brands might be: good, fresh Arabica beans are similar in many ways, up to roasting. Some people prefer a light roast, others medium or dark. Once you decide, find a brand that does what you like consistently.