To my eye, and the opinion of several gunmakers I've known, flat top checkering is the most difficult to properly execute. All flat top diamonds need to be the same size to not be distracting. Sharp diamonds can be overcut and never be detected. Also, from a practical standpoint, sharp checkering can be a real hinderance to a proper mount. When mounting and shooting a double gun both hands are moving a lot. The last thing I want is for sharp checkering to grab the hand, interrupting the mount and swing or moving the hand for a second shot.
Here's a great example of perfect flat top checkering. On my Greener from 1872. Only about 10 lines to the inch but very attractive and practical.
