Tl;dr: both work. From the ssh_config man page: Configuration options may be separated by whitespace or optional whitespace and exactly one `='; the latter

Tl;dr: both work. From the ssh_config man page: Configuration options may be separated by whitespace or optional whitespace and exactly one `='; the latter format is useful to avoid the need to quote whitespace when specifying configuration options using the ssh, scp, and sftp -o option.