Lite XL (lite-xl.com) is also extremely fast. Also, because a lot of it is written in Lua, you can very easily extend it yourself; you can just monkey-patch many functions and do what you want!
It's kind of immature in some ways, for example, the current release version has some limitations in the native plugin interface (which you need for loading C libraries for Lua, as Lite may use a statically linked version), and there is a conflict between the linewrapping and projectsearch plugins where opening a file from it is bugged if you have linewrapping enabled by default.
Lapce does seem more advanced in some ways, but IMO the enormous hackability of Lite is also a nice advantage.
It works quite decently, although again limitations regarding linewrapping apply; the inline lints from lint+ break linewrapping :/
Also, for Lapce I cannot find server integrations other than a few, namely Rust, JS/TS, YAML, C/C++, Go and Dart. No Python, for example. Adding Python support in Lite's LSP is as simple as adding lspconfig.pylsp.setup() to your config (and installing the server), if you already have the plugin set up correctly.
It's kind of immature in some ways, for example, the current release version has some limitations in the native plugin interface (which you need for loading C libraries for Lua, as Lite may use a statically linked version), and there is a conflict between the linewrapping and projectsearch plugins where opening a file from it is bugged if you have linewrapping enabled by default.
Lapce does seem more advanced in some ways, but IMO the enormous hackability of Lite is also a nice advantage.