Which Letter Is Better?

I mentioned a few days ago that the team has been immersed lately in improving the
Office 2007 keyboard model.
We got a lot of constructive feedback around the model from Beta 1 and so we're hard at work addressing it for Beta 2.

Today, I want to just throw out a minor but important detail of the overall design for
discussion to see what you think.

As I mentioned in my original post on the keyboard model, the first step of
using the keyboard with the Ribbon is pressing a letter to navigate to the tab
which contains the control you want to use. For instance, many apps have a
Review tab, and pressing ALT+R puts you in a mode to access the commands on the
Review tab with the keyboard by pressing subsequent letters.

One of the questions we're trying to answer is: What letter should we use for
the first tab of each of the Office 2007 programs?

Allow me to lay out the pros and cons of some of the myriad possibilities.

The first decision: is it important that the first tab of all Ribbon apps
share the same accelerator?

The argument for yes says that certain commands, such as the Clipboard, Find,
Bold, and Italic are almost always on the first tab and therefore if you assign
the same letter to the first tab everywhere, then keyboard accelerators are more
portable across apps.

The counter-argument is that the majority of the features present on the first tabs
are actually different--Excel has Sort and Conditional Formatting, while Word
has Styles and PowerPoint has Slide Layout. And the commands which are consistent already have well-known keyboard shortcuts (CTRL+F, CTRL+B,
CTRL+I, CTRL+X, etc.)

If you do want a common first tab letter, the first thing that comes to
mind would be to pick a letter with a mnemonic hook. For instance, "F" is good for
File because it's the first letter of the word. However, the names of the first
tabs of each of the apps don't have any letters in common. Word is "Write," Excel
is "Sheet," PowerPoint is "Slides," Access is "Data." And Outlook's are totally
variable based on the item type. So using a letter present in all of the words
would be impossible, because there aren't any.

Maybe instead we should optimize around picking a common letter that's easy
to type; after all, probably 90% of keyboard accelerators in Office 2007 will
start with this keystroke. Millions of people will type it millions of times a
day.

So maybe something on the home row of the keyboard? Something on the left side
so that you can hold on to the mouse? Dig up
the research about which letters are easiest to type? "F" and "J" have the
little "home row" dots on them, but F is used for File. Wouldn't people laugh at
us if we gave the first tab "J" even if there's a good reason?

"H" is another possibility, since it's easy to type, you could imagine it stands for "Home," and
sometimes we think of the first tab as the "home tab" because it's
where you will spend most of your time.

Or maybe you go with "S" because it is the first letter of the name of two of
the first tabs (in Excel and PowerPoint). But, if you get used to hitting ALT+S
to access the most common commands, you might get tripped up because in Outlook, the
same shortcut immediately sends the e-mail you're working on. So maybe "S" isn't
the best idea either.

Maybe we should use some other easy-to-type combination, say ALT+SPACE or
ALT+ENTER or ALT+ALT even. Unfortunately, all of them already have
well-established behaviors in Windows or Office which cannot be changed.

There are other factors which go into the design as well, such as
localization issues and the fact that some of the letters are reserved and
cannot be used. But for simplicity's sake I won't get into those here.

So, what should we do? Is it important that the first tabs share a common
letter, and if so, which one should we use? Or, should we pick the letter which
works best for each program (probably mnemonically) and have inconsistency
between the apps? Or something else we haven't thought of yet?

Which letter is better?