The Shorin katas are lighter and faster and suited for a smaller person, or people who like kicking.
This fighting style includes freestyle karate, semi contact, Lau Gar, TKD, largo mano.
The Shorei katas are heavier and stronger and suited for a larger person, or those who like to get stuck in.
This fighting style includes boxing, Thai boxing, FC KB, Judo, Wrestling, Krabi.
In sporting terms, Shorin is football and Shorei is rugby.
The katas are split between Shorin and Shorei.
Shorin includes:
3 Taikyoku
5 Heians
2 Kanku
Enpi
Shorei includes:
3 Tekkis
2 Bassai
Jion
Jitte
Ji'in
Hangetsu
So by the time you have done the first 20 kata, at 3rd dan, you will have 11 Shorin kata and 9 Shorei, a good mix.