While the 808 is a great overdrive, and is about the closest to the original circuit upon which most OD's out there are based, there is no such thing as a "best" overdrive. Different ones do different things tonally, and it depends on what you are trying to achieve with your sound. There are things an 808 can do that a Fulldrive, an OCD, a BB Preamp, etc. won't exactly replicate, but the reverse is also true. Any circuit has its limitations.
Now, if you can only afford to get just one, you certainly wouldn't go wrong making it the 808. It's a great all-around OD, but I certainly wouldn't pay $150 dollars for one, especially since I can duplicate that pedal from scratch for about $40 - $50....and that's if I'm completely out of parts.
Let your ears ultimately choose the OD you want. It's your tone.