>>33405702other answerers have never played these games, here's the correct list:
Normal: spinda
Fire: magcargo or rapidash
Fighting: passimian or crabominable, neither is totally worthless like the three mentioned before though
Water: luvdisc
Flying: fearow (delibird is unironically better)
Grass: sunflora
Poison: swalot
Electric: minun
Ground: wormadam pizza form
Psychic: unown
Rock: corsola
Ice: dewgong
Bug: beautifly
Dragon: drampa (though, like the fighting types, it's not on the same level of shit as everything else listed)
Ghost: dusknoir
Dark: mightyena
Steel: wormadam trash (passimian/drampa situation)
Fairy: dedenne
megas are an intrinsic part of many mons, which is why banette and altaria aren't listed as the worst ghost and dragon types respectively. Drampa, wormadam trash, crabominable, and passimian all have niches in certain tiers/environments, and its important to make the distinction between mons like that and mons like luvdisc.