What are the best type of skewers to use for ground meat kebabs? We like to make ground meat kebabs. I usually use all ground lamb, but occasionally will use a mixture of lamb and beef or lamb and bison. 

I have tried wooden skewers (both small and large) and metal skewers (both round and small flat). (Sizes refer to diameter, not length.)

The problem I have is that if I lightly rub oil on the skewers to prevent sticking, the meat often times gets loose around the skewer and causes the issues you would expect from this. If I don't use any oil, the meat will stick to the skewers.

The meat mixtures we use leans toward Persian or Iranian styles and do include quite a bit of chopped onion. I've thought about adding a very small amount of oil to the meat mixture but I was thinking that it might keep the mixture from holding together as well.

I also considered not using skewers but I like that with the skewers I can keep the kebabs just above the grill grate and don't have to worry about sticking or so much clean up.

My goal is to be able to slide the kebabs off in one piece for a better presentation. Can anyone share ideas, tips, or tricks? Is there perhaps a different type of skewer that may work better?
Easy!  You want fairly broad, flat skewers, which will prevent the meat from rotating around the axis, like these:



Quite appropriately, I've seen these referred to as "Persian-style" skewers.  Not having a decent Middle Eastern grocery nearby, I instead use flattened bamboo skewers that I can find at my local Asian market, which look similar but smaller, like so:



As with any other wooden skewer, you'll want to soak these first so that they don't burn.

The main thing is that the skewers be significantly flat.  Stainless steel versions like this which are quite thin look nice, but they don't grip any better than a round model does.

Alternatively, you can find double skewers which do pretty much the same thing, like these:



If, like me, you bought a massive pack of cheap, round bamboo skewers before you figured this out, you can approximate by using two of them running parallel.  This is basically the same concept as the double skewer without them actually being connected.  The only disadvantage here is that you can find up with twisting if you're not careful, and they're a bit more finicky to use.

It goes without saying that any of these options work very well with just about anything else that you care to skewer and toss on the grill.