(MTG) For infect, if you had to choose one which one would you run?

It really depends on the deck you're running. I'm guessing you have a set amount of cash and are trying to decide which to buy first? I'd have to go with Inkmoth Nexus. Those things are really good especially if you're running equipment or pump spells. If your opponent doesn't have any flyers, it sets them on a pretty short clock.