This one for sure --->
D.I.D Cutting and Riveting Chain Tool
I purchased it and it was the first time ever replacing a chain for me. It's close to impossible to screw it up the way this thing works. If you align the chain into the tool properly, you won't screw it up. VERY easy!
It does break the chain, but as others will likely tell you, the best way to break a chain, is to take a dremel w/a grinder attachment, and grind the flare off of the rivets. Then you can just push the link out. Very simple.