When the antecedent is 'this,' 'that,' 'these,' or 'those,' it's standard to use 'which.'
Literal
Antecedent [subject-が] this, that, these, those [possessive-の] case [topic-は] 'which' [object-を] use [nominalizer-の][subject-が] normal [copula-です].
先行詞 'antecedent' is a grammatical term. More English grammar explanation with Japanese linguistic vocabulary — the rule that demonstrative antecedents prefer 'which' over 'that.' のが普通です is a common way to state conventions: 'the normal/standard thing is to.'