This is a very difficult question to answer. It all depends on whether you value screen real estate for work related stuff, or portability? Yes, the 12.9 inch has been shrunken significant from the previous model and lighter overall, however, it is still rather large for most people.
If you need the extra screen space for productivity or just want a large gorgeous screen to consume content, then 12.9 the way to go.
But if you are like me who intends to use the iPad Pro to do a lot of writing at home and outside, then I definitely need some level of portability. Hence, I chose 11 inch.
It was very tempting to go all out and get the 12.9 inch version, but at the end of the day, you have to carefully decide which size fits your needs.
When I was at the store, I think I spent a good 20 minutes just shuffling back and forth between the 12.9 inch and 11 inch model. I even spent time using the keyboard and see which size is suitable for typing (both are equally good, the smaller one is surprisingly comfortable and just the right size for typing)
So don’t rush and go down and have a look. Hold it, with one hand, two hands, in multiple orientations etc.
Good luck!