I have never taken the opportunity to examine the difference between wellness and well-being, until now that is. I would sometimes interchange these words without knowing which word to use in what situation. (I am a slow learner).
Wellness - One dictionary defines wellness as is an active process of becoming aware of and making choices toward a healthy and fulfilling life. "...a state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity."
Another defines it as the quality or state of being healthy in body and mind, especially as the result of deliberate effort. So, wellness is the total health package: mind, body, and social aspects. There is no mention of spirit in the references that I read.
Well-Being - The best definition that I could find to describe well-being was one by Martin Seligman in his book "Flourish". He states that well-being has five elements: positive emotion, engagement, meaning, positive relationships, and accomplishment. The cornerstone of his work is authentic happiness which is a term that I like.
Therefore well-being is more focussed on the 'spirit' it would seem. Well-being is the intangible stuff that is difficult to measure without conducting assessments whereas wellness is something that you can often see. These are wide generalisations, I know. But that is how I find it easy to remember each one.
Which is better for you, wellness or well-being? I think neither, they go hand-in-hand. While you can have one without the other you really do need both to lead a balanced life. If you are physically fit and are healthy it is much easier to undertake well-being activities. If you are feeling 'down' (poor well-being practices) it is more difficult to undertake a healthy life because of lethargy, lack of meaning, and negative emotions.
I embrace the holistic approach in the programmes that I run. You get a bit of everything. Why, because you need both and they should be undertaken concurrently to get the fastest result at improving your total well-being. Or is that total wellness!
In short, do everything that you can to keep yourself 'well' and don't worry about the terms.