I own one of each.. As far as best bang for the buck , I think the 306 wins. If you want a customizable and even faster charger for multiple batteries and you don't mind some extra cost get the Powerlab 8. The feature I like most on the PL8 is that it can discharge almost twice as fast as the 306B. Both are great choices both will do what you need to do will and both are being used by the ECL community. I use both constantly and interchangeably. Both can do multiple batteries with paraboards or those multi battery charging cables.

I also vote for the Power Lab 8.  When I got mine it almost took time to charge out of the question and really helped with battery management as placing unused flite batteries back to storage is pretty fast. 

Russel,
 I misread your first post I thought you were comparing pl8 with I-306B The PL6 has a similar discharge rate to the 306B and defiantly slower then the pl8. All are great chargers all will require a powerful high amp 24v power supply to get the max out of them. I still have some repurposed server supplies on hand if you eventually need one.
William