Personally, when I design costumes, I like to design a full-head mask. It's more challenging to do so, and the end result can be awesome. I'd rather cover the face than allow it to show through, unless the costume I'm designing is clearly human. The majority of my costumes, though, have been full-head masks and accompanying ensemble. They are very restrictive, very stuffy, hard to see out of, and very, very hot, I can assure you that. I don't envy mascot characters at all, or anyone who needs to stand under hot stage lights in a full costume.
Anywho, I've been monitoring this topic to an extent. The discussion of costuming is fine, and I would rather it stay there. If it starts going into fetishes, though, this bugger's getting locked.
QuickEdit: I changed the title to something a bit more broad. Now, let us move away from the icky connotations associated with fursuits and to a general costuming topic of discussion.