Depends what you want to do with your lighting automations.
I didn’t realize legrand has a home automation option, but look at what features that offers and if that meets your needs.
Lutron caseta and ST now have an official integration that’s been up for a few months and works pretty well (I bought some caseta dimmers and switches after the integration went live). You can search in this forum for topics that have already been created to discuss the caseta integration (the official one, there are other unofficial integrations that community members created and posted about before the official one was available).
So if you value native integration with ST, caseta has that, legrand doesn’t (AFAIK).
Yes, lutron hub is needed. Depends on your definition of native integration. Official integration is a more accurate word, I suppose.
“Stability” is difficult to generalize, because everyone’s setup at home is different in terms of devices, complexity of automations, possible sources of radio interference, etc.
You’ll probably find a lot more people in this forum with experience using lutron caseta, since as I mentioned it integrates with ST. TBH I’ve never seen anyone discuss legrand’s home automation line here (doesn’t mean nobody ever has, you need to search the forum with some keywords if you haven’t already).
Both are good systems, but the LeGrand radiant line is intended to work with their own Intuity home automation platform and there is no integration with SmartThings at all.
Lutron offers the SmartBridge ( note: for technical reasons, this is a bridge, not a hub, just like the Philips Hue Bridge). With the SmartBridge, you can have an official Lutron Caseta integration with SmartThings, as well as with IFTTT, Amazon Alexa, Google Home, and a number of other partners.
Again, they are both good systems, but if you get radiant then you will be using their Intuity platform. Not SmartThings. Legrand Intuity uses a manufacturer proprietary profile which is not compatible with anything else.
Lutron also uses a proprietary protocol, but they offer their SmartBridge product to allow integration with many other systems.
Lutron makes good products, but myself I stuck with Leviton z wave plus devices, so I did not need to have multiple hubs/bridges. Sounds like Legrand would really lock you down to their platform only, which would defeat the purpose of Smartthings being so open.
One advantage that the Lutron Caseta line has is that most of the models do not require a neutral wire. This can really help with retrofits an older houses. But of course the con is that there is an additional bridge device required. So different people will choose different switches. Choice is good.
There’s a discussion of different switch features in the device class FAQ. The light switch discussion starts around post 40.
Lutron is basically the only easy option when you do not have a neutral. I got lucky were the majority of my switches have neutrals. I did have some 3-ways that only had a neutral in one box and was able to use one of the traveler lines from the other box for the neutral. Choice is why I picked the Smartthings hub with so much development.
From a conservation on Reddit, a few suggested using an open z-wave dimmer like GE 14294 or Homeseer WD100+. Point was these integrate directly with ST as opposed to closed protocol like Radiant and Caseta.
I’m also concerned about the white of all products used matching.