Can't say anything about Anker, since I haven't used them. But I have the OWC/NuPower one in my Late '08 I just sold to my brother, and it runs great. I usually get around 3-4 hours out of it which is on par with the stock Apple one when it was new. Never got close to the 5 hour mark unless it was in Word with the brightness way down.
Now I have to consider one for this Early '08 BlackBook I picked up off eBay. It came with a brand new battery, but its one of those cheap $15 Chinese batteries that is glossy and doesn't even fit right, Lol. As far as I know though Anker doesn't have a black one, so that will make it OWC by default. Or Apple, but that's another $30 or so, and I trust OWC with everything else.