i own an octa rdm 38mm and its just such a comfortable watch to wear. today I had a chance to try on a friends cs 40mm and other than the 40mm not being a very proportionate size, feeling big and flat, its too thin as well with the crown digging into the hand. the octa has a good width though so the crown doesn't bite into the skin. i hope the following pictures help and would recommend you try both watches and see which one fits you better and sings to you. Regardless of the model, I would recommend the 38mm over the 40mm.
From an aesthetics angle, they both are good looking watches to me with the octa edging out the cs somewhat. the big date and cool 5 days PR also work for me too.







this assessment not taking into account what you have in your collection currently and what you intend to get in the future. Eg. if you say you intend to buy the resonance next year, then go with the CS. but if you say i just want one good Journe to start and may not ever buy another, then the Octa rdm just might be it.