I lived in Mardon in my first year but that was the year before they started building Holland so we had all the facilities in hall. It was amazing I loved it! As far as atmospheres go it was second to none! and I don't think that now they share a bar and dining room with holland is a bit negative since they still have their own common room! Its the smallest hall but not in a chlostrophobic kind of way. I was in a shared room and loved it. My roommate and I lived together for the whole 3 years we were in Exeter and are still very close! I think in the smaller halls you make a wider circle of friends.
Just becareful when applying to Hope (and possiby lopes but not sure). Main House Hope is beautiful and has the bar there. Lopes and Kilmorie don't have a bar they use the one in Hope. But yeah Main house hope is lovely but it there are also annexes which are just old houses that have been converted! These are nice and in them you do get a nice community again but they are small groups of you and you may feel a little isolated from other people.
And its not the case that Mardon (and Holland) is full of sloanes! Every hall has it's fair share! And most of them aren't as bad as people say and the ones that are don't mix with everyone else anyway!
I'd say between Exeter Halls (hope etc) and Mardon go by where your department is! So Language students, physics, maths and engineering! go for Mardon. Social sciences, business, English, humanities and Law go for Law that way unless you want to use the sports centre you don't have to climb the hill as much!