Should I Register 2020 Vinyl Re-Release or 2005 Original CD?

Dear Rich: My band released a CD in 2005, and we never filed Form SR or PA for the album and underlying works. I am planning a vinyl reissue (with expanded artwork) this year, the songs are in the same order and have been remastered, but the artwork will be slightly different. Should I file the SR and PA for the 2005 release? Or should I treat the 2020 vinyl reissue as a new entity?  

If you're filing Form PA separately (Form PA reflects songwriting), it doesn't matter whether you use the  CD or the vinyl because the compositions are the same on both. (The date for the song publication would be 2005.) In order to register a group of published songs as one "unit of publication," you must meet certain rules.
If you're filing the Form SR separately (Form SR reflects the sound recording), we think you should use your newer remastered vinyl because that is the best sonic version and you will likely use that for downloads going forward. 
If you qualify to file the SR and PA as one application (or you need more information), you'll be best served by using the vinyl version as deposit materials. You can find more on these filing regulations in our Music Law book and in the music copyright lectures, we recorded for Lynda/LinkedIn. 

P.S. Dept. In case you weren't aware, you acquire copyright regardless of whether you register your music. However, there are many benefits to registration.