How easily particular letters are heard (or misheard) can be one consideration when choosing a Vanity callsign.

This Air Force study looked at the intelligibility of each letter when phonetics are used and in the presence of random white noise, which seems to me makes it especially helpful to determine how well the various letters can be heard thru a pileup or in rough conditions. I have pasted what i find to be the key info in the table below, to see the full study please use the link below it.

TABLE II

Intelligibility Scores of the Twenty-Six Alphabet Words (when Masked by Random White Noise)

November 91.16
Romeo 87.67
Whiskey 85.14
Sierra 80.54
Uniform 78.89
Bravo 78.58
Delta 77.62
Tango 76.55
Foxtrot 76.24
Yankee 72.89
Charlie 72.22
Lima 71.58
Pappa 70.45
Mike 69.22
Hotel 68.69
Oscar 67.86
Echo 66.98
Quebec 65.49
Kilo 62.96
Victor 62.67
Juliet 61.77
Zulu 61.67
Golf 58.06
Alfa 54.95
x-Ray 54.25
India 28.67

source:
https://apps.dtic.mil/dtic/tr/fulltext/u2/404051.pdf