It says here that Redis is superior to Memcached, but I plan to update to upgrade my store to the latest Magento 2.3
Will Redis still work? Can't risk slowing the shop down
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Redis is better. Why?
If you already check the redis is better for speed then So go with Redis is the best options.
Magento Docs is already suggested to the use redis.
Refer to Why Redis is better for a list of advantages to using Redis.
I do not think redis will create at Magento 2.3 version.
If you don't already know which one to use, I simply recommend using Redis. It's what's popular now and has more useful features than Memcached. They're interchangeable, and it won't slow your shop down. Caching is used to increase performance, so I'm not sure why you're concerned about speed.
You can read about a good review here: https://stackoverflow.com/questions/10558465/memcached-vs-redis.