Yeah I feel like the Turn A and 00 Qan[T] are easily the top competition here with a Unicorn alongside. Almost nothing is more lethal, Turn A has Moonlight Butterfly while the ELS QanT can freely teleport, and arguably adapt to any possible form of damage or threat due to the ELS in it.
The strongest Gundam is the one with everything mentioned. We never saw the Turn A's other equipment. Imagine if it had its own perfect pack that let it fly as fast or faster than the Victory 2 and had cannons stronger than the DX that could also shoot as far if not farther than it. Imagine if the handheld weapon of the same perfect pack was a stronger GN Sword V that could perform a GN Raiser Sword easily. It's very possible because we know it used to have optional gear that could freeze opponents in place and that could be an upgrade to the G-Self's Tractor Beam.