For now, probably Vera from MiCasa Verde. Very popular in Europe, but zwave-only. Similar price. Every system has different pluses and minuses, so read up. Most z-wave devices you got for a Vera system would also work with SmartThings if you decided to switch later, assuming ST did make a European frequency hub. Vera makes both US and European frequency units, so make sure you get the one you want and that all the devices match the hub’s frequency.
Just be aware that Vera, as a zwave-only system, does support some “scene controller” devices that don’t work with SmartThings. This includes some multibutton wall switches and some handheld remotes. So if you do plan to switch eventually, don’t overinvest in those. You can always ask in this forum for what Devices would be compatible with both. (Most regular wall switches and the Aeon Minimote handheld remote work with both.)
Zipato and Fibaro are also popular Zwave controllers in Europe, but they cost more than the vera. So again, just research Before buying.