If the Gear S3 had Bixby three months ago, or had a solid date when it would get it, I would have gone with the S3 too. But I used Siri a lot with my Apple Watch, and I now use Assistant a lot with my LG Sport. But that danged S Voice on the S3 just didn't cut it for me. I would imagine the S4 will launch with Bixby and I'll be taking a close look at it (assuming Apple doesn't blow me away with the iPhone 8, and then maybe back to Apple Watch to go with it ). The S3 improved on the already-good S2 so I would imagine the S4 will only continue that trend, barring any "explosive" issues.
Mike
yeah, S voice is terrible. That's the one thing I miss from my Apple Watch, having a decent voice assistant. I get by without and just use Google Assistant on my phone if I really need to dictate something (or Google Home in my house for alarms/timers, etc.)