I went back through my history as a trainer and decided to test and see what type I have used the most over the years. here were my results

least used to most used

fairy type

none, not only was fairy type a late addition but I've never been too fond of the type. not even any of the pokemon that later became fairy type, so I've simply never used a fairy type on any of my playthroughs

bug/rock/poison: 3

yeah throughout my travels I haven't used many bug, poison, or rock types, only three of each

rock type

rhyperior (platinum)

dusk lycanroc (ultra sun)

dreadnaw (sword)

bug

scizor (platinum)

ariados (moon)

centiskortch (sword)

poison

alola muk X2 (sun and ultra sun)

ariados (moon)

ice: 4

ice is a pretty late game type so it makes sense that I haven't used that many. I doubt many people have used many ice types on their playthrough teams

mamoswine (soulsilver)

walrein (XD gale of darkness)

dewgong (shiny) (platinum)

froslass (sheild)

dragon/dark/ghost: 6

more late game types, again it makes sense why I haven't used many of these

ghost

decidueye X3 (sun,moon,ultra sun)

alolan marowak (sun)

lunala (moon)

froslass (sheild)

dark

houndoom (XD gale of darkness)

zoroark (white 2)

alolan muk X2 (sun and ultra sun)

malamar (ultra sun)

obstagoon (sheild)

dragon

salamance (XD gale of darkness)

latios (omega ruby)

garchomp (platinum)

zekrom (white)

noivern (ultra sun)

komo-o (sheild)

normal: 7

it's a pretty boring type, but it kind of serves as a nice filler, or jack of all trades type pokemon

pidgeot (soulsilver)

ursaring (XD gale of darkness)

delcatty (omega ruby)

starraptor (pearl)

unfeazant (white 2)

snorlax (y)

obstagoon (sheild)

electric/psychic: 8

now we're getting a bit higher, psychic and electric pokemon have a ton of appeal and the former especially can be found in great abundance

psychic

espeon (XD gale of darkness)

latios (omega ruby)

alakazam (platinum)

swoobat (white)

slowbro (sun)

solgoleo (sun)

lunala (moon)

malamar (ultra sun)

electric

ampheros X2 (soulsilver and XD gale of darkness)

cosplay pikachu (omega ruby)

luxray (like everybody who played pearl)

zebstrika (white)

zekrom (white)

magnezone (white 2)

boltund (sheild)

fire/grass/fighting: 9

two starters and a very fun type to use (one that is often paired with starters) checks out

grass

sceptile (omega ruby)

breloom (omega ruby)

serperior X2 (white and white 2)

chesnaught (y)

decidueye X3 (sun, moon, and ultra sun)

fire

magmortar (soulsilver [didn't eveolve until post playthrough])

houndoom (XD gale of darkness)

infernape (platinum)

talonflame (y)

alolan marrowak (sun)

emboar (moon)

centiskortch (sword)

cinderace (sheild)

fighting

breloom (omega ruby)

machamp (pearl)

infernape (platinum)

throh (white)

chesnaught (y)

lucario (y)

grapploct (sword)

komo-o (sheild)

water: 10

the most common type, as well as a starter, and one that was near manditory for all generations from 1-6, of course it's going to be high up

feraligatr (soulsilver)

gyrados (shiny) (soulsilver)

walrein (XD gale of darkness)

empoleon (pearl)

dewgong (shiny) (platinum)

blastoise (y)

slowbro (sun)

vaporeon (moon)

cramorant (sword)

dreadnaw (sheild)

steel: 11

probably an unexpected type to be this high up, but steel is a versitile and imporant type for any team, you could even go as far as to say it's near manditory, espiecially now with the advent of fairies (plus some of my favorite pokemon are steel type)

empoleon (pearl)

steelix X2 (pearl and Y)

scizor (platinum)

excadrill X3 (white, white 2, and sword)

magnezone (white 2)

lucario (y)

solgoleo (sun)

corvinight (sheild)

and the two types that tie for the most amount of usage is.......

flying and ground: 12 each

I mean....just look at my username....this feels like desinty

ground

mamoswine (soulsilver)

groudon (omega ruby)

steelix X2 (pearl and Y)

gliscor X2 (pearl and white 2)

rhyperior (platinum)

garchomp (platinum)

excadrill X3 (white, white 2, sword)

mudsdale (moon)

flying

gyrados (shiny) (soulsilver)

pidgeot (soulsilver)

salamance (XD gale of darkness)

staraptor (pearl)

gliscor X2 (pearl and white 2)

swoobat (white)

unfeazant (white 2)

talonflame (y)

noivern (ultra sun)

cramorant (sword)

corvinight (sheild)

so of the 78 pokemon i've used on main teams 24 of them were either ground, flying, or both, which may not seem like much but that's about a third of the overall total and keep in mind there were not fairy types so this was out of 17 not 18 types. let me know in the comments below what your most used type was. I'm interested to see.