Rule reminder
When a perception verb has an object that is replaced by a pronoun, the pronoun moves to precede the perception verb (not the infinitive). The past participle of essere/avere verbs agrees with the pronoun when it precedes 'avere'. Example: Ho visto Maria arrivare → L'ho vista arrivare (not 'Ho visto arrivare-la').
In modern spoken Italian, which form is increasingly common even if traditionally non-standard?