The best hanging straps for hammocks are ones that are specifically made for hammocks, such as those offered by Eagles Nest Outfitters. Outdoor gear suppliers such as REI offer a wide selection of highly rated straps for hanging hammocks, both indoor and outdoor styles.
The Kammok Python Straps are very highly rated by customers on the REI website. They also sell the popular ENO Hammock Suspension system.
It is important to make sure that hammock straps are rated for the amount of weight of the users. Using a strap without a sufficient weight limit can lead to hammocks collapsing and causing injury or straps wearing out much sooner than they should.