Bottom line here is that there is no ideal sharpening angle. I have over the decades seen angles as fine as 15 degrees and a wide as 30 degrees recommended for pocket knives. The finer angles seem to be more popular.
A lot depends on how you want the blade to function. A fine angle tends to operate like a razor and slice well. Down side is that given the same steel fine edges don't last as long as wider angles. Thinner angles are more prone to damage if used for scraping, cutting materials with mixed densities and brute force use like batoning.
Wider grinds act more like wedges and operate well for chopping and use as a chisel. They support the edge better and so hold up to hard use, scraping, abrasive materials, and using the edge to pry up flakes. To the bad wider grinds can require more force to get through fibrous materials and cuts through delicate materials can tend to tear and distort.
A lot depends on personal preference, what your doing, and how you're doing it. If you like a super sharp and delicate blade a finer grind is what you want. If your handier with a glorified lawn mower blade swung with brute force and ignorance to chop through everything from raw meat to concrete your going to want a wider grind.
My preference is for something like eighteen to twenty-five degrees. The exact angle is seldom a concern and plus or minus a degree or two makes little difference in function. Consistency of the angle your holding as you sharpen and along the blade is much more important than the exact angle.
A friend claims the 'along the blade' angle is not important as he sharpens his pocket knife with a fine angle in the tip, where a lot of fine work gets done, and a fairly wide angle closer to the handle, where your more likely to use it as a wedge. I could never get the hang of such a variable sharpening angle but it works well for him.