A few from our trip a few years ago, a mixture of aires and off grid spots, can't really decide which is best as they all have their merits. Check them out on streetview with the coords....
Tregunc - Ster Greich 47.84066 -3.89693 5 pl 24hr max
Tregunc - Pouldohan 47.84087 -3.89678 5 pl toilets for thetford 24hr max bit like a caravan club cl
Plonevez - Porzay, Plage de Kervel 48.11565 -4.28033 Elevated parking area overlooking beach. 8 pl 48hrs max, sloping.
Ploevez - Porzay, Trefeunyec 48.13043 -4.26787 quiet bay, bins, toilets/wc another spot at 48.13433 -4.26820 raised parking area overlooking bay.
Tregarvan - (le passage) 48.24561 -4.20092 overlooking estuary, quiet, wc/pissoir don't park in from of houses, parking best along gravel track that runs adj to sea to the west where there is a nice little pull in.
Tregarvan village 48.25081 -4.22978 parking slots opp estuary between slipways. Charming little hamlet and church.
Tidibi (Hopital Camfrout) 48.30139 -4.24902 dead end road between nice little coves. Double tap near entrance.
Trevou - Treguignec, Port le Goff 48.82127 -3.36431 No facs.
Moriex Chapelle st Maurice/Plage st Maurice 48.52879 -2.63177 No facs, nice views of bay, slipway to beach.
Motorhome parking area in car park at Dinan, 48.45415 -2.03835 free on Sundays but can be busy, alternative is the free aire at Lavallay, about a 15 min walk from there to Dinan but we didn't do the actual walk. 48.45425 -2.03026
If you do a search for "Brittany" and select posted by me ("DBK") you should get a lot of returns and if you have the time it might be worth looking through the ones which seem the most promising, probably those which were made as part of a longer trip. We've been there several times so you might find some places of interest. Expect aires to be busy near the coast, especially the free or cheap ones - the French love 'em!
You don't say what actually you like or what you want from these aires, do you want to visit nteresting towns /villages or more rural with vista's , or beach's or castle etc.
Huelgoat , Rochefort en Terre , La gacilly , Malestroit , Rose Granite coast , carnac , Quiberon the list is endless
Fougeres is a nice free aire no ehu & gets busy but nice town with lovely castle
Pont Rean Guichen nice river side aire 6 euro no ehu
Caramet sur mer nice aire 6 euro , 400 yds to nice view of the bay lovely walks down to beach & old fort
Brambel aire Piriac sur mer 6 euro . nice beach side aire gets busy , if you like moules
Campeneac aire free by a small lake/pond by junior school , nice village services in village payable
Pouance nice aire if you want peace and quiet lakeside aire in as back yard not actually Brittany , it's Pays de la Loire
We don't do a lot of coastal aires but here's some we have done plus some inland ones by water.
all in camper contact
63051 basic car park with seaviews , long walk down & back to beach free
1185 La plouha room for about 20 , 100yrds to beach free
1262 small aire behind town hall 150 yrds to fab beach free
1198 caramet sur mer 400 yrds to cliff top veiw fab then long walk to beach or old fort 6euros incl ehu
when on your way or way back nice car park 48.258369 -4.554874 free great beach
1193 parking on sandy terraces ( care not to get stuck in) 7.2 euros
2131 aire on headland beautiful rugged cliffs & walks 15 euro's
we didn't stay over night just parked at a cost cant remember how much , we stopped free at 3477.
22831 out on the rugged coast road bit rural but nice beach a lot of surfing free
42982 brambel @ piriac sur mer gets busy lovely spot across the road to beach 6 euros
41134 st cast le guildo cliff top location over looking harbour 7 euro
now some inland
1172 Treguier nice riverside aire free no services
1221 Locronan beautiful village bit touristy aire 9.62 euro with ehu , we didn't stop overnight but did day visit
19864 v.rural canalside aire with toilet , but we use the parking area on opp side of road down a lane .
24578 Tinteniac canalside 4 euro nice
1169 St Thegonnec nice aire & town
11402 Fougere nice castle & town free
24378 Malestroit riverside aire not much but river walks nice
25229 La Cheze by small resevoir 4 euro weekdays w/end free incl some ehu
21152 Bourg Blanc nice lakeside aire free
22640 nice small lakeside aire facilaties payable up in village