I see there’s two switches available for the same price, the switch and the dimmer. Since the difference is not well explained on the site could someone tell me why would I want one instead of the other? I would use them mostly with smart bulb but I’m looking to have the most versatility and you never know what light fixture I might install in the future.
Thanks in advance.
I see three White Series products on their site now:
The community threads linked to above will probably answer more than I can recall from any project off the top of my head (they have a lot going on now!) or possibly even by refreshing my memory from any. 
Following up on what @BertABCD1234 posted, I think you have to match the model to what you are controlling.
Controlling an AC fan . . ceiling? You want the fan switch.
Controlling a dumb bulb and want to dim it? You want the dimmer.
Controlling a smart THREAD/MATTER bulb? You want the dimmer.
Controlling something else that you can’t control with a dimmer where you need a relay-based switch (such as an a LED strip controller, light with a ballast. exhaust fan or something else where you just want on/off capability)? You want the switch.
Wrong link to the thread on-off switch, this is it - Thread / Matter On/Off Switch | Project Vernacular
This switch could run fans with only on-off control. Probably a better fit for exhaust fans then the fan switch which matches with ceiling fans better.
Adding more to the above, you may not care about protocol at all unless you want to Z-Wave Association, Zigbee binding, or Matter binding if/when hubs or devices support it (I’m not aware of any at the moment that do, and I’m not sure it will be quite the same as Zigbee if different protocols are involved since you’d need a TBR in between at least). This is important to some people because it still works if your hub is down (the hub isn’t involved after initial setup, if at all), may be faster, and so overall reliability or acceptance-factor ratings may therefore be higher.
Others prefer the power that putting a hub in the middle provides, and if you’re using a hub that processes automations locally (SmartThings is famous for not in many cases), this can also be pretty fast. In this case, the switch/dimmer would just be another device on your hub, and you can create an automation to control whatever device of whatever protocol. This is my preference, so I don’t match my switches/dimmers to my bulbs — I just get the protocol I want to build out my Zigbee, Z-Wave, and soon to be Thread meshes and the devices (bulbs, sensors, etc.) that fit my preferences.
But in any case, it is absolutely important to consider the type of load you’ll be putting on the switch/dimmer — that was my main point above, perhaps not clearly stated.