For simplicity’s sake this is comparing Pokemon at full health..
Also Pokemon that can only be obtained by breeding, evolving a Pokemon etc. don’t count for this question as they’re not ‘caught’ in the traditional sense.
Pleaselog inorregisterto add a comment.
All below Pokemon have a catch rate if 255, which is the maximum.
Generation 2161 Sentret163 Hoothoot165 Ledyba167 Spinarak187 Hoppip194 Wooper
Generation 3261 Poochyena263 Zigzagoon265 Wurmple270 Lotad273 Seedot285 Shroomish287 Slakoth290 Nincada299 Nosepass300 Skitty322 Numel325 Spoink327 Spinda328 Trapinch333 Swablu343 Baltoy349 Feebas363 Spheal366 Clamperl
Generation 6659 Bunnelby661 Fletchling664 Scatterbug
Generation 7731 Pikipek734 Yungoos736 Grubbin795 Pheromosa798 Kartana
Source