Guitar friendly and piano-friendly keys

The above listed 22 keys can be grouped into guitar-friendly and also piano-friendly keys. Some keys are neither piano or guitar friendly (eg. Db-Major), which does not mean they don't use them in guitar or piano songs.

In the guitar friendly keys most of the basic chords (ie: I, ii, iii, IV, V, vi) can be played as open chords, without barre, where the index finger has to push down 5-6 strings simultainously. The most frequently used open chords are:

A, Am, B7, C, D, Dm, E, Em, G.

The guitar friendly keys range from one flat (d-minor, F-Major) to four sharps (E-Major). If you browse though the songs of Deacon, May and Taylor, you'll find that nearly all of their songs are written in guitar-friendly keys, even the ones that were written on piano or synth.
There are many guitar songs that are not in guitar friendly keys. The majorirty of these songs use alternate tuning (Eb-tuning, capo) or varyspeed.

The so-called piano friendly keys are ranged approximately from one flat (d-minor, F-Major) to three flats (c#-minor, Eb-Major). Many of Mercury's piano songs are written in these keys, but far not as exclusively as the others preferance of guitar friendly keys.
The keys that include 2 or 3 black-key notes on the piano anatomically match up better with the human hand. The pianist can keep their shorter fingers (ie. thumb and pinky), on white keys and keep their longer fingers on black keys. It's a more natural position for the fingers than the key of C, which uses all white notes, and which forces you to contort the hand a little more. This explanation applies for the more advenced players. Rooky players need years to recognise the pianofriendliness of these keys. For them the pianofriendliness means that each basic chords have the same black-and-white key pattern.