So funny you post this because I had the same dilemma and just recently ended up purchasing the Caro vs. Chanel Boy. I began to research both bags on purseforum and watched numerous YouTube videos. I can share my thoughts and what led me to purchase the Caro.
From reading the Chanel threads, a lot of people seem to be put off by Chanel with constant price increases, bad customer service and some questionable quality. Some Chanel fans have even noted not feeling safe with their bags worth $5k+(seems mostly in bigger cities). That said, Dior of course is still very high end and luxe but maybe still less known and flashy than Chanel, plus I have a more casual lifestyle.
As for longevity, the Chanel Boy I think will be around much longer than Caro. It’s going on now for 11 years I believe. Dior seems to discontinue their loved bags often. Other than the Dior Lady, maybe the Saddle, the rest of their bags are questionable and resale of Dior bags is not that great. That being said, the Caro still has the timeless cannage leather, so it will still be a type of classic Dior.
I absolutely love the cool and effortless look of the boy and planned on getting the black with ruthenium hardware, however, trying to find the perfect one pre-loved proved to be a difficult task and sometimes even more expensive than new ones in boutiques. I don’t have a Chanel SA so it seemed almost impossible. I ended up purchasing the Dior Caro black with Ruthenium hardware, which seemed a bit more casual than the gold Caro.
Also, it seems both Dior and Chanel will have price increases mid January and for Chanel the boy is specifically mentioned.
Hope this helps! I will always love the Chanel Boy, and may still obtain one, but ultimately decided to go for Caro based on budget (I really wanted a new bag, not pre-loved) and personal style.
. I ended up purchasing a medium as i felt that i could store a little more without the tight feeling as i plan to get an insert. I would suggest to try both bags and see which one makes your heart flutter 
