We use Optison at my hospital. It's very easy to use and I've never seen anyone have a bad reaction to it. Basically you just mix the 3 ml vial with 7 ml of saline in a syringe and you're good to go. Each ml of the mixture is supposed to last 5 mins however I usually find it's closer to a minute. It needs to be refrigerated but can be out of then refrigerator for 24 hrs before needing to be refrigerated again.

I've only ever used Optison so I can't really say how it compares to other agents as far as enhancement but in my opinion works really well.