I tend to vary which I choose, depending on the content of the table and also the surrounding content. The judgement is partly aesthetic and partly usability.
For example, if I have a table with only a small amount of content I might choose autofit to content, as the extra white space caused by fit to width might look weird. Conversely, if there are several tables on a page, having them all different sizes might look weird, so I'd choose to make them all the same width, including column widths where possible.
Whether I set column widths depends on the content, and if I decide one column needs a width set, then I'll set widths for all the columns in the table. For example, if I have a description column, it is likely to have a lot of text. I would want to minimise the amount of wrapped text for that column and so set it to, say, 40%. I'd then set widths for the other columns so the total of all columns is 100%. I can't remember why I do this; the reason is lost in the mists of time. Note that the column total will be 100%, even if the table itself is set to say 90% - the table is saying "give me 90% of the available topic width", whereas a 10% column is saying "give me 10% of the width inside the table boundary". Hope that makes sense.
These are all my opinions based on what I like, rather than any sort of studies. I also can't comment on print, as I haven't written for print for a long time - I'll sometimes print a few topics, just to make sure they aren't completely borked, but I don't do specific design for that output.
Thank you, Amebr. That's just the information I hoped for, and appreciate