I generally try 'Estimate' with a 2 radius, 0.3 softness and 0.2 artifact suppression first. It typically works pretty well on my landscapes, but if I think it is being too aggressive I will switch to Generic and play with the radius, leaving artifact suppression at 0.2. Radius usually ends up between 0.9 and 1.3.
Yes, 'Estimate' sometimes works fine, sometimes not. It depends on the subject and the location of the focus plane. It's too bad one cannot import a custom made PSF kernel. Maybe something for the long overdue updated version.
I virtually never use the built-in optional 'classic' sharpener, preferring to do that elsewhere. Maybe I should give it a second chance. Does it work as well/better than what you can typically achieve later in the workflow?
No, not necessarily. It's just that one shouldn't try to do everything with only a single deconvolution pass. For very good control over subsequent 'Creative sharpening', their 'Topaz Labs Detail' plugin is very useful. It's like adding Clarity on steroids, to be used with restraint but very powerful.