As others have said, with all the numbers in a typical plog, the "garbage-in, garbage-out" risk is very real. For me, it means that any method that *only* has me input numbers, and give me numbers as output without a visual check as to whether stuff makes sense, is a big no-no.
So for my flight planning needs I use both ends of the scale, but not the bits in the middle:
One end of the scale which works for me, is the PPL-taught way of doing things. Line on the map, use ruler and protractor to measure distance and true track, use the E6B to convert into magnetic heading and ETE. When doing this I can continuously visualize what I'm doing and whether I'm correcting for drift the proper way. And there are various other gross error checks built-in as well.
At the other end of the scale is a full-blown navigation package. SkyDemon in my case, but anything electronic that allows you to see your full route on an electronic map, and which outputs a complete plog would be fine. As long as I can see a line from my departure to my destination, and see in the plog that the (downloaded) wind values are more or less in line with what I would expect, I can be reasonably sure the magnetic headings and ETEs that the program calculated are correct.
But I don't like anything in between, such as a CX2 or any of these iPad/iPhone "E6B" calculator apps. The risk of input/output errors is too big for my liking, and there are no implicit gross error checks built into the complete method.