It's Always best to use the lowest base type possible. This gives the implementer of your interface, or consumer of your method, the opportunity to use whatever they like behind the scenes. Today, you almost always use IList, the primary reason for IList to still be around is for reasons https://rafaelqbkqx.mysticwiki.com/783762/c_ilist_nerelerde_kullanılıyor_ile_ilgili_detaylı_notlar