I usually pour off what I can after letting it settle out a bit, but don't pour too much; the healthiest yeast will generally still be floating about, depending on how long you've let it sit/chill. When in doubt, I just pitch everything, just to be safe.
I usually make my starters 36-48 hours in advance. That way they are usually at, or just past, high krausen. I pitch the whole thing after a good swirl to make sure all the yeast is in suspension.
I always let it settle out pour off the wort while leave just enough wort to make yeast slurry. I have never liked the idea of pouring unhopped wort into my wort. For ales is not to bad as the size of the starter is usually 1 - 2l. But with lagers it can be 1 gal or more that you are pouring in.
I've been chilling in the fridge for a day or so and then pouring off the wort and just pitching the slurry. Just make sure to warm up the yeast a bit if you are doing ales. The sudden shock is maybe not so good for the yeast.