As of right now (since the game is tomorrow), I'm going to take Create Opening, since that seems to fit my play style a little better. If I end up not liking it, I'm sure the DM won't mind me switching it out for something else.
I've used this power, and it's quite good. Assuming you are a tough fighter with good defenses who can take some hits (and not an Eladrin pumping Wisdom or something with light armor), it is very useful. It allows your strikers to get in, hit something, and then you can get them out.
The other thing no one has mentioned is that this marks the target with a minor action. If, for example, you need to use your Standard action for a Second Wind, you can still mark a target with Create Opening, or use it to mark a second target.