It also massively depends on the people you get. People put with people who get on with each other will give the impression of a better atmosphere than people put with people who don't get on - whatever halls they are in. Its the same in any halls so i wouldn't worry about atmosphere just yet as that comes when you make friends... regardless of whether or not they're in your halls.
Choose a hall depending on your own personal standards, wants and 'needs'. If you think you want an ensuite then by all means apply for one, don't let what anyone else says here sway it. I wanted an ensuite and i applied for one, got one and was really glad i did. That said, there was no way i needed it and could have coped quite happily without it! If you want to go self catered - go self catered! I'd advise going down to look round all the halls if you can tbh (though im sure there are hundreds of photos floating around here showing the real halls, not just the ones staged for photos!) personally, if i'd have showed up to lafrowda on my first day, i wouldn't have moved in...!
Basically, everyone on here has their own set views of what makes the exeter experience amazing. Go with your instincts and then everything else will fall into place x