Key Value is often the most readable and size efficient format

Output

python

{1: 'one', 2: 'two', 3: 'three', 4: 'four', 5: 'five', 6: 'six', 7: 'seven', 8: 'eight', 9: 'nine', 10: 'ten', 11: 'eleven', 12: 'twelve', 13: 'thirteen', 14: 'fourteen', 15: 'fifteen', 16: 'sixteen', 17: 'seventeen', 18: 'eighteen', 19: 'nineteen', 20: 'twenty'}

json

{"1": "one", "2": "two", "3": "three", "4": "four", "5": "five", "6": "six", "7": "seven", "8": "eight", "9": "nine", "10": "ten", "11": "eleven", "12": "twelve", "13": "thirteen", "14": "fourteen", "15": "fifteen", "16": "sixteen", "17": "seventeen", "18": "eighteen", "19": "nineteen", "20": "twenty"}

xml

<1>one</1>
<2>two</2>
<3>three</3>
<4>four</4>
<5>five</5>
<6>six</6>
<7>seven</7>
<8>eight</8>
<9>nine</9>
<10>ten</10>
<11>eleven</11>
<12>twelve</12>
<13>thirteen</13>
<14>fourteen</14>
<15>fifteen</15>
<16>sixteen</16>
<17>seventeen</17>
<18>eighteen</18>
<19>nineteen</19>
<20>twenty</20>

key value

"1"="one" "2"="two" "3"="three" "4"="four" "5"="five" "6"="six" "7"="seven" "8"="eight" "9"="nine" "10"="ten" "11"="eleven" "12"="twelve" "13"="thirteen" "14"="fourteen" "15"="fifteen" "16"="sixteen" "17"="seventeen" "18"="eighteen" "19"="nineteen" "20"="twenty"

Summary

json: 303 which is 13 percent larger than key value

xml: 293 which is 3 percent larger than key value

key value: 262