There’s a good FAQ on CoRE and webCoRE here:
https://community.smartthings.com/t/faq-what-is-webcore-and-what-was-core/59981
I only used CoRE a few times before switching to webCoRE, which I use a lot. Both are good, but webCoRE is more powerful, is updated more frequently, and I feel like there’s more community support for it.