I do both, as well.
It depends on the prayer, and where you are.
Sometimes, if the church is crowded and folks are moving about, and kids are playing with their toys, and people are chit chatting, it's easier to simply block them all out by closing your eyes and focus on the "sounds", not the "sites". Then you hear the hymns being sung, the words of the priest's petitions, you notice the sweetness of the incense, etc.
However, if there's no major distractions, open and look at the salvation before you. The icons, the priest's gestures, etc. It's communal prayer.
It all depends.
However, I've heard that the faithful are not to "imagine" things, and not "visualize" things...which is apt to happen with closed eyes. If they are open you have a harder time of visualizing, as your mind is locked on what your eyes are looking at.
I am curious if there really is a right or wrong here.