Welcome to FT, hardworking21!
If you book on United ticket stock, your earning won't change based on which flight number you book, though it does matter where you book. The common wisdom is to avoid codeshares whenever possible, though, so I'd recommend booking the OS flight number unless there's a compelling reason to do otherwise. If you book on Austrian ticket stock, however, your RDM earning will be based on distance instead of price. You'd have to evaluate which one of those would give you better earnings. Also, I'm pretty sure you'll only get PQD if you book on United ticket stock or with a United flight number (PQD are meaningless to me, so I may not be current on those rules).