Welcome to Flyertalk!
Both FFPs have some advantages, though I personally much prefer Aeroplan.
In order to better help you some additional info would be helpful:
- What airlines do you fly?
- What fares do you usually book (discounted economy/economy/business/first class)?
- Do you mainly fly domestically or internationally?
- Which benefits are most important to you? (lounge access, upgrades, mileage redemptions etc.)