My husband just got back from Toulouse and stayed at 2 of the 3 hotels.
The CP is by far the nicest of the 3. The location is fantastic (right on Place Capitole, walkable to almost everything you'd want to see). As a Plat, he was upgraded to the club room (not huge but nice) with lounge access. (I've also stayed there in the past, and the rooms facing the Place have a really nice view.)

The other two choices are near the airport (so not convenient if you want to be in town, near restaurants, etc.) He had all sorts of problems at the HI. He was given a crappy room (even though he had reserved the "executive room") and they insisted they had upgraded him! After much discussion, they finally moved him into the room he was supposed to have. He said it was much better than the regular rooms, but still not on par with the CP rooms.
There is, of couse, no exec. lounge, but they do have complimentary continental breakfast.(and airport shuttle)

Don't know anything about the HIX. I'd say if you don't HAVE to be right by the airport (like for a very early flight), the CP is the clear choice. Especially if you're going to be there for several nights at a time. Hope this helps. (Oh, and I've got pictures too, if you're interested )