I don’t own both bags but I tried them on before. As mentioned above, it’s really up to you to decide which style you want to go for. Diana’s are super elegant and can be rather delicate (considering they will be more than 20 years old now), so it’s definitely not a good idea to overstuffed it with heavy things. However, if you are able to get hold of a good condition vintage, the lambskin is very soft and supple.
Two of my friends recently got the Chanel 19 and I played with them for quite a while. I don’t like how goatskin feels as it does feel plasticky at times. (I like the lambskin ones tho) However, it’s a more casual style and lightweight. It can pack a ton too! People keep saying it’s going to be in the classic line because it’s the Karl’s last bag for Chanel. I don’t buy it though. Frankly speaking I don’t think it will look very nice after heavy use of 10 years or so because of its slouchiness. Nevertheless, it will be a bag that sparks joy for the years that you can use it.
I love both bags but I feel like getting a diana more because I just love how it feels in the hand! I also not a fan of the bulky chains on the 19. But again, this is just up to my personal preference.