I have two.
Well, three if you count the cheap tyrolean (probably pear wood?) a friend brought me from the Czech republic after visiting there. It's a cool conversation piece for non-smokers, but I fire it up very rarely. Maybe once a year, when my kids ask me to smoke it because it looks cool.
Otherwise, I have one of those cheap Iwan Ries rusticated ones. I like it a lot even though the draw is too restricted. One of these days I may play with opening it up.
The other is from an old Bewlay stummel I had lying around for years. It had originally been a bent billiard, but hadn't had a stem for a long time. I finally sent it to Mike Myers and asked him to make a churchwarden of it. He did a great job.
Like others have said, the cooler smoke canard helps justify things, but doesn't seem to hold up to any noticeable degree.
Nevertheless, I really enjoy my churchwardens for the reason others have cited -- the exaggerated leverage lets you move the stem however you like with mainly wrist motion, while your arm lays on a rest. It's lazy, but pipe smoking for some of us is about comfort and relaxation at the end of a day, and boy is the churchwarden well suited to reading, watching a film, or staring at the fire.