Arms There are 5 different options for your Remix Chair arms:
No Arms Pretty self explanatory.
Plastic Loop Arms 9.5" above the seat (10" if you opt for the thin seat foam) these arms do not adjust at all. You have 20.75" in between armrests.
Aluminum Loop Arms Exactly the same as plastic but fancy polished aluminum.
Height-Adjustable Arms 6.1" - 11.3" in range for placement above the seat (6.7" - 11.9" for thin seat foam) and 21.5" between the armrests. All you do is lift a lever on the outside of the armpad to adjust arm height.
High-Performance Arms These also offer the same height-adjustability as above as well as pivoting armpads that are width and depth-adjustable. They adjust 2" in width (1" per arm) 1.5" in depth and pivot 45 degrees. The inside distance between the armrest ranges from 15.5" - 23.3".
Which should you go for? It really depends on your needs. Most people opt for the high performance arms for several reasons. The features allow you to rest your shoulders and maintain an ergonomic posture no matter what height you or your desk is. It also allows you to quickly move them out of the way when exiting the chair.