I'm guessing you took the ending in ME3 where you took control of the reapers?
Well I have no quarrel when blowing those sick *BEEPS* to hell. But the Catalyst was using flawed logic in an unsolvable problem and had a point. The peace wouldn't last. As horrible as the Reapers were they were literally the best case scenario. They slaughtered millions upon billions yet they thought they were making sure organic life continued to live on. And in a weird way they did. When it would inevitably happen again, these new synthetics would probably not be as sympathetic or have the same motivation as the Reapers.
Control doesn't solve the problem, just one of the side-effects. BUT with Shepard as the AI, the Reapers now have the closest thing to morality as an AI can have (like EDI). Also I hated destroying EDI & the Geth after trying so hard/long to get them and the Quarians to work together.
Synthesis is ideal but it's also amoral to an extent and I really wouldn't want all of those husked species to have self-awareness. Husks, Banshees, Brutes and Cannables part of society? I'd actually feel SORRY for those guys.
If the Reaper forces were "salvageable" in a way I'd agree with synthesis as the best of the 3. But I still wouldn't want the Reaper AI in control so I'd plan on control first then Synthesis later. Screw you, catalyst!