I'll jump in as well. S9 unlocked ( my first unlocked) on VZ and the S9 has been a fabulous phone. Updates are usually a few weeks behind and I'm just not that impatient that an update is a life changing experience if I have to wait. That being said, I haven't really seen any big advantage to unlocked other than to switch carriers and no plans on that any time in the future. Probably will just go with the carrier version next time.
A little iffy on updating to the S10, it's pretty damn expensive and I don't like using a payment plan. Have to see what the S9 to S10 trade-in looks like with Samsung, which by the way was effortless with my S7e last Spring. I tend to be an early adopter and some of the tech coming out after the S10 looks interesting so I may wait through my two OS update cycle on my S9. We'll see how compelling the features and the trade-in program for the S10 work out....
Let me just say my Samsung device experience over the years has been flawless and I love the integration with the Samsung TVs in the house through SmartView. Very pleased with their products....