I use both formats. Mostly the one with the added random suffix, though. If somebody were to figure out that my domain is an alias and I used only non-obfuscated aliases, it would be easy to figure out how my aliases for the other services could look like. Adding a suffix makes it impossible to guess. I sometimes use aliases without suffixes if I want them to look better to the recipient, or it's an alias of more importance to me, or if I need to remember it more easily, etc.