As I understand it, all email addresses held by PPrune are encrypted and therefore 'crawlers' will not find them. As 'Mutt' says, the generation of email addies is largely automatic and you will almost certainly get spam on whichever one you use. I had loads on an AOL address (random numbers/letters only) which was only ever used to register with AOL. When I inspected the address header, it was full of close 'similar' computer generated addresses.
I and others have before recommended 'Mailwasher' which was free and enables you to easily separate and either bounce or delete spam before having to download it. Although it was free, I would urge anyone who uses it to make the small donation to the author!