Well to be really technical, 2300 Jackson Street was the 6th Jacksons studio album however we all know Michael had left the group as a full time member by this point (if we can put it that way). Here are my thoughts, I limited it to two offerings from each LP.
The Jacksons
Blues Away - can't possibly miss this one out. It may not be the strongest song on the set, but as far as Michael's genesis as a songwriter goes there's really no where else to start this list. This is the first commercially released Michael Jackson composition and the only one to feature until Heartbreak Hotel years later. It's also noteable for many of Michael's vocal trademark hiccups etc. making early appearances in the closing of the song.
Style of Life - I chose this one again as it's the only other track on the album that Michael has a songwriting credit for, this time with Tito. The lyrics are achingly prophetic at times if you really listen and although other songs on the first album have the distinction of being more well known or bigger hits (Enjoy Yourself, Dreamer, Show You The Way To Go) I just couldn't omit this.
Goin' Places
Even Though You're Gone
and
Find Me A Girl
Typical Gamble & Huff pieces, chosen on the strength of Michael's vocal performance on both.
Destiny
That's What You Get (For Being Polite) - testament to the growing prowess and maturity of the brothers'/Michael's songwriting abilities. Swathes ahead of anything that had come before in terms of lyricism and storytelling for me.
Shake Your Body (Down To The Ground) - duh. Dance music landmark.
Triumph
Heartbreak Hotel - well known and clearly beloved to Michael given that it's the only Jacksons-credited track he kept in his concert setlists for a good 10 years. Only the second solo composition by Michael to be commercially released and therefore the precursor to his solo compositions on Off the Wall and, although Michael never wrote it, sonically the foreward to Thriller. Too important to miss.
Can You Feel It - duh again. Probably the most effective world-conscious song Michael ever had a hand in writing. Controversial? The blueprint for all the others that followed.
Victory
No brainer here, Be Not Always and State of Shock. To me these are like MJ solo songs that he 'donated' to the project given the brothers' are limited to backing vocals and Marlon only to 'additional' lyrics for Be Not Always. Backed up further by the presence of Bruce Swedien and Matt Forger. I think Michael also had a hand in The Hurt but as far as the album goes as a whole his presence besides singing is at it's lowest ever.
--hope this helps!