Assuming a password manager is used, even jfav0ohjau4gvncgan19@domain should be OK.
On the other hand, I might just be overthinking it. It could even look suspicious to customer support, or is that again just overthinking?
Also, there already will necessarily be some predictable ones, such as work@domain, although servicename@domain would provide even more possible matches.
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.