This is a funny thread with lots of opinions. In the end these trucks really are not well comparable and you should decide whether you want to go for the 'cool and unique' or for the more practical.
A 77 sure is nice. As said, it will need a turbo, parts cost more and are rarer, and it has less space.
The 80s are plentiful, the 1HDT is a great engine (a 2 year old can change the BEBs), lots of space, lost of aftermarket support, dirt cheap parts from wrecked US 80s. And the seats are better for a semi old guy with a questionable back by a mile.
To call an 80 less capable off road is simply nonsense and will depend on how the truck is built and the driver. It's hard to stop a locked 80 though.
The H151H is a fine tranny. Yes, it could use a taller 5th gear. No, it won't break. I had one apart very recently and it is without doubt as beefy if not beefier than the H55F. It shifts fine and will last as long as the engine, and is easier rebuilt than the H55F.
Get what makes you happier. If you won't stop smiling when sitting in a 77, get the 77 and smile.
cheers,
Jan