Having looked at the documentation, bcrypt.net-next seems to be a port from BCrypt.Net, with some sensible improvements.
Maybe the most important improvement is compatibility with other platforms, e.g. PHP with its
$2y signature. The BCrypt.Net source code doesn't seem to support this signature.
The advantage from pre hashing of long passwords is somewhat theoretical, passwords longer than 72 characters are more than strong enough to be truncated, on the other side, pre hashing could make your hashes less compatible. As I understand it, the pre hashing is only done when using
BCrypt.EnhancedHashPassword() instead of
BCrypt.HashPassword(), which seems to be backwards compatible.
bcrypt.net-next is built with Dotnet Standard, so it should run cross platform.
So I would go for bcrypt.net-next then, I cannot see any disadvantages.