The best porn is like the best mainstream movie - a completely subjective opinion. Unless you have no idea what kind of porn you like you'd be better off giving folks some idea of what works for you first.
If you like nasty anal scenes, all the "Winkers" and "Milk Junkies" (1 and 2) are the best. Belladonna's movies are great too (specially "Fetish Fanatic" and "Fucking Girls" series). But well, is just my taste in porn.
Almost any director in the Evil Angel Empire is worth space on your developing shelf of titles.
My personal favorites from that company are the old-timers (performers that became true erotic artists); John Leslie, Christoph Clark, Joey Silver and of course John Stagliano. Rocco's titles are amazing too! Some are feature oriented (with a story) but most are gonzo (sex, sex, SEX!).
I think a lot of people checked this thread in hopes of finding the name of the best porn ever. This one should have been titled, "Best Porn Ever?" but anyhow I'd suggest most anything over the last few years from Jonni Darkko. If you are an anal fan you've got the Anal Trainer series, for cock sucking you have the Suck It Dry series, for big boobs you've got...and so on. Mike Quasar also puts out some great stuff - mostly for Zero Tolerance.
I forgot the name of my other favorite director. I just can't remember!
ADT has a few lists for the best of 2006 in this thread and this one too!
I would go with the last Rocco videos that he actually starred in. He knew he it was his last; so he gave it his all! Very, very hot performances for all in the scenes! I don't know the exact year but my guess is around 2005?
It really is so much a matter personal taste that it's hard to offer much reliable guidance. But, just personally, I would also endorse the Jules Jordan stuff: the Ass Worship series if you like anal and higher gloss production, and the Weapons of Ass Destruction series for more of the same though with toys.
There's so many great films it's impossible almost to give advice.
Michelle Wild is one of my favourites. Browse the ADT reviews - you could hardly go wrong with anything she starred in. She was very pretty with gorgeous natural breasts and she loved to fuck and suck. Here is a review of Crack Her Jack 1:
Corruption won the AVN Award for Best Feature Movie Video and also won the top stop on DVD Talk's top 20 of 2006. It is a feature surrounding a gonzo movie, so it is worth a watch. I loved it and consider it one of the best of all time. Hillary Scott was awesome.