hi
let me give you my experience since i am one of the rare people that had used both 12.9 and 9.7inch models.
my experience was that i started with the 12.9inch so it can be travel companion. for work and play it was good (other than those accelerometer games)
Then when i change jobs, where i didn't need to work on the go so much, i traded 1:1 for the 9.7inch model. Great for media consumption and some work, but i could not do side by side work like typing on one side and reading using split view because it was too small to read.
Now I am thinking of changing back to the 12.9inch because of split view and the amount of side by side work i need to do.
my recommendation is that you evaluate your use pattern. the 9.7 inch is probably the best ipad you can get. but for productive work, the 12.9inch is king for tablets. Especially if you use the split view often like me. you will be in love with the large screen.
Tip: what i did was get the 12.9inch with the smart cover keyboard and instead of adding more weight with a back cover, i went to sim lim and got it 'skinned' with clear by tough film. cost me about $20 but good to keep weight down and protect against scratches.