I'd say this would be a good problem to have, I can't envision a scenario where they will both be available especially with more teams playing 3-4.
The size difference is not all that great (Jordan, 6041 287 35 in arms -- Watt 6053 290 34 in arms) and they actually have a lot of similarities as players (both use hands well, they are good pash rushers and also can affect passing lanes when they can't get there, good aray of pash rush moves, strong lower body, good balance, good lateral movement and both play the run well. Both are durable). Jordan has experience in 3-4 and as DE while Watt less experience although he is more versatile (plays special teams, DT on four man line) and Jordan is stronger in the upper body. In terms of character, Watt has formed his own charity while Jordan was suspended one game in 2008 for DUI suspicion.
Too close to call at this time is my opinion but it would be a good problem to have while on the clock.