Jon,
I have used the Deere 673 tiller(6 ft) with both the 820 and 4520 tractors without problems. Since the 4520 has more power I can maintain a higher ground speed with it. With a 1520 you should be fine running most tillers in first or second gear. I also have a Howard 66" that I bought for the 820 and can pull it in second gear for most jobs.
About the KingKutter, lots of people here on TBN have them and recommend them. I have looked at them closely and they seem to be well made, this may be a good way to go and save some coins.
Haven't looked at Countyline tillers, don't know about them.
There are lots of good tillers out there to choose from and I would give consideration to the short lines that my local dealer handles. It helps to have some where to go to get parts if needed.
