I have the 85mm f/1.8, and it is a great portrait lens! I'm very happy with it even though I've been thinking about selling it to help fund a 70-200mm f/4L IS USM lens purchase. Of course, probably the most important factor is going to be your budget.
Are you looking for a dedicated portrait lens? The 70-200mm IS lens (f/2.8 and f/4) are very sharp lenses, and some photographers do not want that for their portraits.
Judging from your lens inventory, I would think the two 50mm lenses you already own would perform very well as your portrait lenses. If you can really put to use the 70-200mm L lens (other than portraits) and afford it without breaking the bank, I would probably go that route.
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