Dirty Mind to Lovesexy, honestly, is an out-of-this-world run. I can put on any album from that streak and it feel that it (mostly) shows Prince at his best. At any point, I might call any one of those albums my favorite P album... 8 albums in as many years. Few folks run their critical period for that long with that much output.
Controversy is probably my least favorite of that stretch. From the perspective of great runs, that infuriates me -- because it basically means Dirty Mind can't be included, which is in my gun-to-the-head top 3.
Keeping the question of runs at bay for a moment, I don't think I could really make a gun-to-the-head top 3. But I can organize the period into three tiers:
Personal favorites (i.e. what I listen to and actively appreciate most): SOTT/Parade/Dirty Mind/Lovesexy
Classics that I love but honestly don't reach for that often: 1999 and Purple Rain. I'm more partial to the latter; 1999 has always seemed a bit bloated to me (but what do you take off!??!).
The easiest for me to "let go" of: Controversy and ATWIAD. ATWIAD *almost* makes it into my personal favorites list but I skip Temptation, America, and The Ladder too easily.
With all that in mind... total personal preference, but my streaks would probably be:
5 albums: Purple Rain to Lovesexy 4 albums: Purple Rain to SOTT 3 albums: Parade to Lovesexy
If we're talking more "objectively" classics, that might all change. At least the 5 album streak, that would probably be 1999 to SOTT.
I don't know man, thanks for letting my brain procrastinate on everything else for a while, lol...