I primarily use 3 different thread options:
Ritza Tiger thread is considered the superior thread among leatherworkers for its durability and strength. It is 100% polyester and lightly waxed making it UV resistant and dependable. The thread will lie flat against the leather.
Vinymo MBT is a unique, bonded polyester thread. It's twisty and it stays that way because the strands are tightly wound and internally bonded. I hand wax this thread prior to stitching.
XianGe is a fine bonded polyester thread that I use for Ultra fine stitching.