I'm sure all of Joe's CD's are good....

That's probably the toughest question I've come across. I first saw Joe when he was touring "Had to Cry Today" and I was blown away when he played the title track live. I wish he still played it live.

Here's my opinion, for what it's worth:

Live from Nowhere in Particular and Royal Albert Hall are both great starts because there are various styles and sounds showcased. I think it depends on what type of music you are looking for in particular. No pun intended. "Bloodline" is a great rock album even without taking into consideration that it was done by a bunch of kids!  "A New Day Yesterday" is Joe's first solo effort and it pays a great deal of tribute to his influences with some great songs written by Joe as well. "So It's Like That" is a solid rock album. "Blues Deluxe" is probably the most traditional blues album Joe has done, but he definitely puts his own label on it. It's also very consistent. "Had To Cry Today", "You & Me", and "Sloe Gin" are all similar, but each album brings something new to the table and is more polished than the last. "The Ballad of John Henry" is a heavier and darker album. I would say it's probably Joe's most consistent.  If you're looking for some great harder rock, go "Black Country Communion". "Black Rock" is cool because of some of the Greek influences in the music. "Dust Bowl" is great too! It sort of takes me all over the world with the storytelling on each track. Try demoing on itunes, then buying from Joe's store. That way you can really find out what does it for you.

On a side note:

Usually, Joe's albums combine an English blues rock cover or two (think Tea For One, Sloe Gin, Had to Cry Today, Spanish Boots, Another Kind of Love, Cradle Rock even though Rory's Irish, etc.), a few songs which are penned by Joe which either have lyrics or are instrumental (Miss You Hate You, Blue and Evil, Django), and some covers that Joe always puts his unique spin on. Never thought I would see Joe cover Streisand on Dust Bowl, but it totally worked!