For Fall Out Boy it's a tie between "Sugar We're Goin' Down" and "What a Catch Donnie", My Chemical Romance is probably "House of Wolves" or "Honey This Mirror Isn't Big Enough for the Two of Us" (what a mouthful) and... yeah, Panic! At the Disco is probably "I Write Sins, Not Tragedies". I never liked Panic! much, I just remember the 3 used to get compared a lot.
And I agree, Fall Out Boy is a pretty solid band through and through, and they continued to get better with time. My Chemical Romance bounced off in a direction that I wasn't too alright with, but they were having a lot of internal issues so I think that was to be expected, along with their breakup which I'm still pretty gutted about. My Chemical Romance was definitely my thing when I was like 13 though.