There are three popular options.
First, The Fibaro RGBW controller is a Z wave plus device available on either the US or UK zwave frequencies. This is a well engineered device with a number of additional features and works well with smartthings.
The second is the Gledopto zigbee controller. It is less expensive than the fibaro, but with fewer features. It has the self certifying CE Mark. Be careful when shopping for this as there are many look-alike Chinese copycats which are not as safely engineered and may have no safety mark or a counterfeit one. (Fire safety is an important issue with this type of device, and you don’t want to save a little money only to increase your fire risk.) this device is sold under several different brand names, but look for the photographs of the back and you should see both the gledopto name and the CE Mark.
https://www.amazon.com/GIDERWEL-Controller-Lightify-Controlled-Include/dp/B07NQC5V3S
The third option is to get one of the various Wi-Fi choices. Some of these are better than others, and again you have to be careful about cheap knock off’s with no safety rating. Getting these to work is a much more complex procedure than the previous two because you have to flash the firmware on the device before you can even start to have it talk to smartthings. You can read more about these models and talk to people who are using them in the following thread
[RELEASE] SmartLife (H801) RGBW LED Strip Wifi Controller & Bulb
So it really depends on what you were looking for. The Fibaro is a solid high-level device with many features. Since it uses zwave, make sure that you get one which exactly matches the frequency of your hub. You can’t use the US Fibaro model with the SmartThings UK hub or vice a versa.
The gledopto is A less expensive device with fewer features, but popular, particularly for those who want to use zigbee.
The Wi-Fi devices are much less expensive, but you have to really do your research on these to make sure that you are getting one that will be safe to operate, and the integration with SmartThings is much more difficult to set up.
As @fido mentions below, a fourth option which lets you use the inexpensive Wi-Fi devices but only provides limited integration is to choose a Wi-Fi controller that has an IFTTT channel and then you can use that for indirect integration. It skips the complex technical setup since you don’t have to flash the firmware, but you’ll have to create virtual switches for pretty much any color combination that you want to use so it can be a lot of work in that way.