The Joy-Cons for Switch have got a lot of well deserved criticism for the simple fact that they are very prone to drifting, meaning that your character on screen will move in a direction even if you don't touch the analog stick. Fortunately, this seems to have been rectified, despite Nintendo previously saying they hadn't changed anything.
In a Q&A over at Nintendo.com, the deputy general manager Toru Yamashita explains:
"The degree of wear depends on factors like the combination of the materials and forms, so we continue to make improvements by researching which combinations are less likely to wear. We mentioned that the Joy-Con controller specifications hadn't changed in the sense that we didn't add new features such as new buttons, but the analog sticks in the Joy-Con controllers included with Nintendo Switch - OLED Model are the latest version with all the improvements. Needless to say, so are the analog sticks included in Nintendo Switch, Nintendo Switch Lite, separately sold Joy-Con controllers, and the Nintendo Switch Pro Controller that are currently being shipped."
Basically, newer Joy-Cons should be more durable and have all these improvements, including the Switch OLED that was launched today.