We're talking about a form in datasheet view? I'd say you answered your own question from the first post - choosing best fit or double clicking on the column border will auto size to the widest value on screen. When you think about it, it's not necessarily a bad thing. For example, if you had a thousand records on the form and only intended to scroll through 50 or so, why would you want the width to be based on ones you can't and maybe won't see, especially if this means you'll now end up scrolling left & right through columns that are wider than they need to be? Then again, if we're talking about a table, it shouldn't be a concern at all.
If a static width value isn't the way you want to go, you'd have to get the length of each field based on the records returned, which I'd probably do as calculated query fields. But a lot of bother for very little return, methinks.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.