Right, I understand that Sovereign would be the easiest method as they'd essentially catch everyone by surprise before they'd have a chance to even fight back. However (maybe I'm not remembering this correctly) but I thought the Reapers are described as this nearly unstoppable force? At the end of ME1, doesn't it take a huge galactic force just to take down Sovereign? How would they be able to handle a fleet of Reapers?
I guess my point is, if the Reaper fleet is that powerful, it seems they should pretty easily be able to kill everything, surprise attack with Sovereign or not. It kinda makes me feel that destroying Sovereign really wasn't a big deal to the Reapers.