Currently I use postgres with BDR at clickup.com, and am going to do the same for gitdash.io
We've definitely run into some issues with it, but I think it was a good choice in the end. I've used a few different dbs in production and this has been the best. We can pretty easily migrate the db and add/remove columns to tables as necessary, which is very necessary since we make a lot of pretty large changes. This was an issue in cassandra, we couldn't pivot some of our ideas easily and to use cassandra to its best potential you kind of need a defined schema and query plan from the beginning. Postgres is also super easy to use if you know SQL already.
I've also previously used mongo and couch db in production. Mongos lack of transactions made it a bad choice for my current projects IMO.
Making a db choice is definitely difficult, and I'm no expert in it, but I think if you go with one of the larger relational db names you won't necessarily be making the absolute wrong decision.