the carnac area is our favourite. weather is a bit better than further north. beg meil - it rained the whole time which has made us biased, but given the choice i would go to carnac.
you have the standing stones at carnac. golf du morbihan is pretty. men du beach is one of our top beaches anywhere - and we live by the coast and are fussy.
grande metairie have been to about 3 times. it will be busy but does have a lot of things to do sport wise and a good pool.
vanne and auray are lovely towns (parking is likely to be a problem perhaps).
if you get a detailed map you can find quiet beaches off the beaten track. there was one slightly north of carnac - long stretch of sand, with practically no-one there. we picnicked in a field of orchids.
quiberon - only been there off season as does have reputation for being busy. we found lots of other places and nice beaches to go to anyway so couldn't be bothered to return to this part.
the other campsite might be worth considering - i've not been there - and the pitches sound smaller. there have been reviews on here. but it does have the advantage of being walking distance to men du beach and the supermarket - if you are worried about traffic. just off the main road where its located there's a nice area with bars/restaurants - we missed this the first few times we visited
guites are really boring. even my 2 year old got bored.