Subjunctive Mood - Expressing Past Regrets

How does one describe regrets about the past? In other words, how does one express the idea of, "I should have..." There are several ways in which you will hear this idea expressed in Spanish:

The first example, which is the most formal of the three, uses the following formula:
debiera/debieras/debiera/debiéramos/debierais/debieran + haber + past participle
Debiera haber lavado el coche. - I should have washed the car.

The second example uses a very standard construction which adheres to this pattern:
debí/debiste/debió/debimos/debisteis/debieron + haber + past participle
Debí haber hecho la tarea. - I should have done the homework.

The third example, which is the least formal of the three, uses this formula:
hubiera/hubieras/hubiera/hubiéramos/hubierais/hubieran + past participle
Hubiera prestado atención a mi papá. - I should have paid attention to my father.

There are many factors that will determine which of these three constructions you should use. There are not only regional differences among the three, but there are differences in tone as well.