Don,
I have both. I have a '74 6 and a '69 B. I've also owned a '78 B in the last year (sold it), so I could literally get out of one car and into the other to compare. I love both cars for different reasons. My '69 B is undergoing a restoration right now so it's not on the road. My 6 is a great looking driver and it gets driven three or four times a month. They are very different cars. For what it's worth, here's my honest opinion about each of the cars and their differences:
The 6 is a more attractive car appearance-wise, but the B is not bad either. The 6 rides rougher and rattles and squeaks. This may be due to frame vs. unibody construction. The B feels more solid...like driving a Honda car compared to the 6. The 6 is much more cramped in the interior and generally not as comfortable. The 6 feels like you're driving a bigger car, though, and is not as nimble as the B unless you do some suspension work (which I have done). The 6 will win hands down in a drag race over the B...especially a later rubber B. B's are plentiful and 6's are getting quite rare. Parts are much more expensive for the 6 than the B and there are more folks selling B parts, so you can shop around a bit more. Spares are easy to find for the B. Both cars have their share of problems. Rust will render a unibody B useless, while frame rot on a 6 is usually repairable. The B has a bulletproof drivetrain while the 6 is a little iffy with lots of folks citing clutch issues, half shaft bind, hub problems and the diff mounts tend to come loose from the frame. The 2500 in the 6 is a joy to listen to as you're driving. The B doesn't come close. B's have tendencies to crack heads, manifolds and burn head gaskets due to the siamese port of # 2 and 3 cylinders. The steering on the B is effortless compared to the 6. That big 2500 sitting on the front tires can make parking difficult, especially for females. If your wife/girlfriend will be spending any time in the car, the B is the better pick. The 6 just seems to be more of a man's car. I say don't pick. Buy one of each and be your own judge. I think they're both great cars and I wouldn't want to be without either one.