The AABA format was the predominant songwriting format in popular music in the first half of the 20th century. Songs in the AABA format consist of four sections, each eight bars long. The A section is the main section of the song--the verse--and it repeats the most often. The B section, also referred to as the bridge or "middle 8," presents a change in mood in the song by often presenting contrasting lyrics and chords. This songwriting format was popularized by Tin Pan Alley, a collective of various songwriters and publishers in New York City where songwriting greats like Irving Berlin and George Gershwin worked. The AABA format died out in the 1960s with the popularity of rock 'n' roll and the rise of groups like the Beatles. Before the Beatles broke off into other songwriting formats, they utilized the AABA format in songs such as "From Me to You" and "Do You Want To Know a Secret?"
The verse-chorus format has been the songwriting format of choice for modern popular music since the 1960s. Unlike the AABA format, which highlights the verse, the verse-chorus format puts emphasis on the chorus. In this form, the verse serves as a buildup to the chorus, which has the major hook and catchiest part of the song. Verse-chorus songs sometimes include a bridge, but it usually only appears once if at all. You can hear the verse-chorus format in a variety of songs, spanning genres, from The Police's "Every Little Thing She Does is Magic" to Britney Spears' "Oops, I Did It Again." The format is so prevalent that Kurt Cobain, who used the format often, almost named a song "Verse Chorus Verse."
The 12-bar form in the AAB pattern is synonymous with the blues. Most blues songs are in the AAB format. Like the AABA format, the AAB form doesn't have a definitive "chorus." The major hook of the song, in which the title most often appears, is in the B section. The AAB form utilizes what are referred to as the I-IV-V chords. The A section starts on the I chord and consists of a set of lyrics sung over four bars. The second A section repeats itself but starts on the IV chord. The B section begins on the V chord and consists of a different lyric, usually a response to the A section, which resolves back on the I chord of the A section. "Dust My Broom," by Elmore James, is just one example of the AAB format.