See, with John being *MilitaryMan* I have difficulties picturing him with Elizabeth or Rodney- that whole US military of no fraternizing with your commanding officer and 'don't ask don't tell' crap. He wouldn't risk it. Teyla or Ronon wouldn't be under his command officially so it's actually possible to see something between him and either of them

I doubt John would be able to be in a relationship with any of them though because he's incapable of showing his vulnerability to someone under his command. In my mind Jack's more of an equal with him so John's more comfortable showing that he might need someone or feel weak or hurt or whatever