In an ideal situation this is what I'd consider:
1) Positioning. What's their heading and angle of attack in relation to ME? Are they just cruising, or are they entering a fight? Are they flying abreast or is one trailing behind the other? Level flight? Climbing? Diving? Turning? Where is MY position? Behind them? To their left or right? Ahead of them?
2) Situational Awareness. Have they given any indication they've seen me? HAVE they seen me? Is it JUST these two bandits or are there others nearby? Friendlies?
3) Which of the two provides a cleaner and more sure shot? If I make a move against one, will his buddy be able to swing in on me?
4) What ARE the bandits? As I usually fly the Corsair, I want to be sure to eliminate whichever target would make the hardest kill if it came down to a close-quarters fight (Spitfires, Zekes, etc) on the first pass. So if the high ENY is a Spitfire, and the low ENY is an ElGay I'd want to nail the Spit first and take him out of the fight, as I'm more confident of being able to deal with the LA7 in an extended fight (that, and I REALLY don't want to deal with yet ANOTHER friggen' Spit HO dweeb

).
5) What's the terrain like? Any cover I can use on approach? They're at 5000ft, but what's ground level? 100ft? 4999ft?