I will leave technical evaluation to those who are best qualified - actual users.
IRIS - In the SmartThings MarketPlace
Monoprice - In the community.
Visionic: (according to Amazon reviews, requires manual device handler installation.
Bosch - unknown.
Switches: 3-Way: I do not know of any Dimmable. If this is to control a single light, consider a dimmable bulb.
Switches: Dimmable: GE are good and not expensive, easy to install.
For bulbs, I prefer that they also have color temperature control (I do not like the 2700K “soft white”. Cost is about $5-10 higher. GE and Sylvania make good Z-Wave and Zigbee options that work with SmartThings.
There’s no one “best” because different people have different needs, preferences, and, of course, budgets. And it also depends on what you want the sensor for. If you want to trigger a light to come on when someone walks into a room, you will need one which is much quicker to respond than if you are using one to give you a reminder that the window was left open and rain is expected. ️
The following FAQ (this is a clickable link) discusses the different features that different device classes might have, and why you might choose one over another. It covers both sensors and switches, so it would be a good place to start.
After you read that, if you come back here and tell us a little more about the specific uses you would have, I’m sure people would be glad to make recommendations.
Also, we do need to know what country you are in (US, Canada, or U.K.) as the devices available do vary by region.
Also, there are many three-way dimmer switches available, including the Lutron Caseta and a number of different Zwave brands. You won’t have any trouble finding one of those, although you will have to replace both the master and the auxiliary switches.
We even have a separate FAQ on wiring the GE brand switches in a three-way configuration, if you do end up deciding on the GE, although there are a number of other brands to consider as well. The FAQ is still worth a glance because it also covers the basic concepts. With diagrams!
I have been fairly happy with my GE dimmers and fan switches. They do NOT seem to like Cree candelabra bulbs but are fine with Cree downlights. For the candelabras (all my ceiling fans) I switched to Phillips warm glow.
I, and many others, have had issues with the Monoprice contact sensors sticking open even after being closed. I also had issues with the EcoLink ones.
The Samsung SmartSense sensors have always been reliable for me. They are more expensive but you get what you paid for. I have 7 leak sensors, about 6 multi purpose sensors, and 5 temp/humidity sensors including one in the refrigerator that all have been rock solid. Only complaint with the Samsung sensors is I have one of the “older” style motion sensors …picks up motion about 20 feet away which is what I wanted but then I got a second one which is a “new” one that you have to be on top of. Not nearly as good as the old style.