In my experience...

Some ways have been traced from satellite images, and are fairly obviously 'in the wrong position', so in that case I would adjust the way to fit my GPS track or the average of the tracks if I don't have one.

When I'm recording a GPS track in my car, then I'm using an external antenna, which is going to be more accurate than a handheld device inside a car, because the external antenna will have a much better view of the satellites than a handheld device inside a car (which can only see the satellites that are visible 'horizontally' through the windows). In these situations, it is also normally obvious that my track is more accurate than most existing ones. The existing ones often tend to be wobbly and don't look like the path a car would normally take, so I assume that they are from handheld devices positioned inside a car. In this situation I would give my track more weight in positioning the ways. Even with an external antenna, it's never going to be totally consistent, or necessarily accurate, so you need to keep that in mind. Even with an external antenna, sometimes my track will veer off or miss out corners.In situations where I can see/feel that my track is not as accurate as it could be, then I will give it less weight.

In situations where I'm walking, using a handheld device (which is unlikely to have an unrestricted view of the sky, however you hold it) then it's also normally obvious where my track is not accurate (i.e. it's wobbly). Then I will use the average of the tracks (excluding ones that look obviously inaccurate - big, jerky lines).

If there is only one GPS track, then it is very likely that it is 'on one side of the road', so you need to work out which direction it relates to, so that you can take account of that when positioning the way.