It seems many people are interested in the comparison of Sia and Storj. I don't think Sia looks Storj as a competitor. Sia only looks the centralized clouds as the competitors such as Amazon S3. The goal of Sia is to over take Amazon S3.

If you really want to compare these two projects, the best way to do so is to check their github activities and run these two softwares to figure it out yourselves.

If you don't know how to check the github activities and you are too lazy to run the softwares you have to rely on other people's opinions. But you still can choose to rely on some reliable sources with data and facts which other people have aggregated. You need data and facts, not just words. Here are some reliable sources for you to refer to:

https://www.coingecko.com/en (projects ranking and pay attention to the Delevoper column)

www.coinmarketcap.com (marketcap ranking)

https://thecontrol.co/meet-sia-a-user-owned-amazon-s3-challenger-that-lets-you-rent-out-your-extra-disk-space-fa9da6ff9223#.9mrlonvf7 (in the middle of this article, there is a nice graph with data to compare Sia, storj, and maidsafe)