I prefer the 77 myself, but we're not here for what we like. The op wants to know which would be best for him.
Now seeing as I have no idea how much experience you have riding or working on a bike I would suggest the 80. I do this because the TCI is much easier to live with. Points can be a big PITA to work with. Being that old the breaker plates and screws are worn. As they wear they get harder to set.
With a Pamco you can eliminate this. But as a first adventure into old bikes the TCI is a better option.
Generally and older cheaper bike will take more work to get road worthy. Either one of those can be made into a very reliable day to day rider. Except for a few things they are about the same bike.
Most of the early issues with handling and brakes were dealt with by 77. After that they made some changes, mostly cosmetic, over the years.
I would recommend getting the one that needs less work to get road worthy. This way you will have less to spend after purchase, get to ride it sooner.
I would also suggest that getting the bike roadworthy and riding it as stock will let you learn about how the bike is to live with.
After riding it for the first summer, fixing things as they come along, and they will, you will have a much clearer idea of any changes you might want.
Several have bought a just to mod into a bobber, tracker, café, whatever, and after the initial riding and fixing they have found they like them pretty much stock. A few mods to upgrade the handling, and increase the reliability a bit.
Leo