Mostly Clairefontaine and sometimes Leuchtturm1917. I recently bought Rhodia dotpads and dotbooks. I also have an Itoya Oasis light notebook and two Apica notebooks, just for trying them.
You can try the squeeze converter, if you don't like you can try the CON-40 converter. It's the only other Pilot converter that can go in a Metro. But it's not a really liked converter... I can't really say because I never used mine yet, I just refill cartridges for my Pilot pens. Which is another option for you.