These days there are lots of options, and different things will work for different people. And even moreso with Matter coming.
From what I’ve seen, hubitat and home assistant are popular alternatives for those with strong technical skills. But for those just looking for a plug and play system with a comparable userfriendly app, the popular choices are somewhat different, particularly if you’re willing to go to new devices.
Alexa, Google Home, and Apple HomeKit have all significantly increased the complexity of rules they can support over the last two years, and some people who were already using one of those (or in the case of Apple, who already have iOS devices) are just going to those. Sure, at least the first two are a lot simpler than SmartThings, but they’re enough for many people.
I would argue that with the addition of Shortcuts, HomeKit has become almost comparable to SmartThings for power users, and if you add virtual devices through a third-party system, definitely close. But typically more stable (the recent architecture upgrade was a failure, but they rolled it back pretty quickly). And with a very big advantage for those of us who need our systems to keep working, the ability to defer updates until their impact is known. The main negative in HomeKit has always been the cost of individual devices, but matter is going to improve a lot of that.
If you can live with only selfbranded Zigbee plus matter, the new IKEA Dirigera system is worth a look. Aqara is another possible platform in this category.
Tuya isn’t for me, and their Matter hub looks like it will arrive a little later than the other superbudget brands, but they have a very wide range of device classes and they will also be an option for some people just for that reason.
If you are OK with only z wave and a few somewhat clunky integrations, the new z-box from Zooz has great engineering and a good visual rules engine.
I’m not specifically recommending any of those as alternatives, I’m just saying that there are quite a few choices these days, and different ones will work for different people.
There will also be people, myself included, who run multiple platforms. As I’ve mentioned before, several years ago I moved my own mission critical use cases off of smartthings because the platform just wasn’t reliable enough for my own needs. And because I really needed the ability to delay updates, since I only have one techie aide, who only comes once a week.
But I still use smartthings for some integrations and use cases, complex convenience situations, where it’s great when it works, and if it doesn’t, we have a Plan B already installed. I don’t know if that would make sense to most people, again, I am more dependent on my Home Automation than more able-bodied folks, but it is yet another option.
Choice is good. The trick is finding a setup that works for your own needs and preferences. And budget, of course.