Unfortunately being a style question, this is very subjective and you will likely have many conflicting results. Moreover, the style to use depends heavily on your usage of TABs or spaces.
As for my two cents, I prefer a variation of the second version. I like this best:
Name : Hamt
Version : 0.1.0
Cabal-Version : >= 1.2
License : BSD3
Author : Jason Baker
It is the most readable and easy to use version that I have tried. The only real downside is that I have to figure out what the widest field is, and sometimes end up having to expand all of them when one is too wide (this usually only happens with CSS). However there are a few points that need to be considered.
First, I usually prefer TABs as opposed to spaces, however the actual TAB setting varies; for example, I am accustomed to 4-space TABs for C(++) code or HTML and 2-space TABs for Pascal or Assembler code, whereas for some things like CSS, I have no preference for the TAB width. This variation complicates things enough, but then the editor I use throws in its own complications. Some editors let you set per-language TAB settings, but some don't (even some that have different profiles).
You can avoid this complication by forgoing TABs in favor of spaces. Since code is usually in a fixed-width font, using spaces works fine, whereas if you are formatting fields in a form, resumé, or other non-code text and are using a proportional font, you'll need TABs to keep things aligned.
I prefer TABs in general because even with fixed-width code, I find it frustrating to have to cursor through several spaces for each TAB. I recall that the old Borland IDEs had an option to cursor through TABs (specifically entire lengths of whitespace) as a single entity instead of as two, four, etc. spaces. That made it practical to insert TABs as spaces while making cursor navigation easy and fast. Unfortunately I have not seen any modern, Windows editors that can do that.
Finally, whether or not others will be using your code plays a big factor in the choice of style. I am usually the only one who uses my code, so I can format everything according to my taste without regard to the editors or settings of others. If you are working with others, you will need to take them into account as they will need to consider you.
In summary, readability is good and very desirable, however the settings and editors you and others that need to use the code will be important when making the decision. If you are alone, you may as well just use the format that is most readable. You may need to get used to using it, but it will likely pay off in the long run, especially when you need to come back to code you wrote a while back: readability is as important as comments in understanding what the code does. If you work with others, then you will want to work together to set out some sort of design guide for use by the team.