We're fortunate to have such a choice.
I selected the 1020 after the 1520 was out. I had wanted the 1020 since its release, but I had been holding out, scheming how I could get a 64gb model in the US. When I was ready to compromise and deal with 32GBs, I was most persuaded by the 1520's SD capability. But, I was pretty sure I did not want to tote a phablet, even though that screen was/is beautiful -maybe if I didn't already have an RT and a 7" Kindle Fire. I was in the store a dozen times making sure that my sense of the 1520's size was correct. It came down to a desired camera vs. unwanted size for me, and compromising on storage. They both are fast, modern, beautiful devices with beautiful screens. I have 4 cases for my black beauty, and I'm very happy with its snug fit in, yet easy in-and-out of, the inner or sub-pocket of my 4 Levi cargo shorts.
Every choice in life involves compromising. Enjoy your eventual selection.