We are having the same debate!
We stayed at OKW last year and the studio was fab, lots of room and having the kitchenette was a real plus. Especially the microwave as DD still likes warm milk on her breakfast!
But, we are booked for off site but are thinking of upgrading to on site for our second week, and I have said to DH that I'm not sure that DD will see OKW as an upgrade / treat as
1 - we stayed there last year!
2 - I really don't think she will realise that we are off site as I don't think she would know what the difference is!
3 - the pool area at CBR looks fab, and very little children friendly, moreso than OKW. So from that point of view for us that's where the "treat" would come in!
As said the CS options are not great at OKW and the TS restaurant is ok, nothing special, but you do have the boat to DTD.
I think overall the real plus of OKW has to be the size of the studios and the kitchenette. How time do you spend in the room, and would you use the microwave and toaster much, as you have a fridge and coffee maker at CBR the same as OWK.
Good luck with your decision
Claire