Depends on your application.
Shottky diodes can be made to double or triple over a wide frequency range, but their conversion loss will always be high--at least 8 db, and typically more like 10-12 db.
Step recovery (varactor diodes) can be used with much greater conversion efficiency, possibly only 2 dB conversion loss for a doubler. But they are narrow band circuits that need to be carefully tuned. One advantage is that they can do high multiplication values, like a X10.