Same here, coming from the iPhone to the Samsung S9. My motivations are that I really like the bezel-less look and resulting larger screen on a manageable size phone, but don't want to pay $1000+ for it. And the S9 supports band 71, which is T-Mobile's future, according to T-Mobile *smile*. In fact, I have the iPhone 8, a fast phone that just works. The iPhone screen is a little smaller than I'd like, but the iPhone Plus is too big physically to fit in a pocket comfortably. When I first saw the bezel-less phones, I figured that was the wave of the future. I was very disappointed that Apple up-marketed their bezel-less model so much that I just couldn't see putting out that much money for a phone. My hope was that they would do what Samsung did with the S8 with the iPhone 8, but no.
Anyways, loving the roomy screen on the S9, especially for the size of the phone. Configuring it has been a little bit of a challenge, but what's life without a few challenges to overcome *smile*? The phone is fast, has all the features that I need, and enjoyable to use. I'm still getting used to the fingerprint reader on the back, but that'll come with time I'm sure.
My only reservation at this point is the duplication of functionality relative to bare Android that Samsung does. I've banished Bixby to the cornfield, and am using Google Messages and Calendar apps, and Chrome. But I cannot disable or uninstall a bunch of stuff that I have no need for, so they just sit there with the phone checking if there are updates for them *smile*. Not to mention that I paid cash for the phone and can't remove the T-Mobile app, but that's another story *smile*.
Got to say that overall I love this phone.