For portraits I prefer the 100 macro, but both it and the 70-200 deliver great results. The 100mm is lighter, faster, less conspicuous, and has more effective stabilization. Those are all good qualities for a portrait lens. Of course the IS will be less useful if you're using a fast shutter speed, but that isn't always the case, especially if your subject is standing relatively still in low light (and using a tripod is not practical). For candid portraits it's better to have more reach, of course, so in those cases, the 70-200 is preferable.
I had the 100mm f/2 before I bought the 2.8L and really enjoyed that lens, but it had some nasty non-correctable chromatic aberration at f/2 that caused me to stop it down most of the time.
At any rate, if you want to have macro capabilities and also want to shoot portraits, you can't beat the versatility of the 100mm f/2.8L. It is a true 1:1 macro lens, is weather sealed, has very effective stabilization (for non-macro distances, at least), and is optically DELICIOUS!