Amy,
While I haven't been in a dedicated 2-br, I think they are equally "nice"; it's just a matter of what you are looking for. If it is for a single family, I would think the dedicated would be preferable; you get at least a chance of 2 queen beds in the 2nd bedroom, and maybe you can guarantee it (I don't recall). Be sure to ask for 2 queens if you want them.
If it's for a mixed party that extends beyond your immediate family, the lockoff is probably more desirable as you can "separate" accommodations by actually locking the door, and have separate entry doors. It takes less points than reserving a studio and 1br separately, and you're guaranteed they will be adjacent.