I recommend sharpening the edge closer to the user as it makes the angle for using the tool easier, i.e., the user can stand more upright. If the other edge is sharpened, the user will have to bend down to use it, and the joy of gardening will be lost.
Sharpen the inside edge using an angle grinder with a 120 grit flap disc. A metal grinding wheel may be needed for shaping the edge if it is in bad shape.
|35 - 40°
||If the original angle is different, it is best to match that, but the angle should be in the range of 30 - 45°.|