Nios VS NiosII

Nios Classic:

- Software development from the command line

- Sliding window register set (jumping to/from subroutines slides the window)

- 16 and 32 bit cores but no core variants

- No branch prediction, used delay slots (when the program counter jumps it executes a NOP since the pipeline is always looking ahead)

Nios II:

- Software development from the command line or Nios II IDE

- Static register set (32 of them)

- 32 bit core with three core variants

- Static branch prediction (s core) and dynamic branch prediction (f core) which helps prevent the pipeline from stalling when the program counter does not move sequentially forward (if, for, while, do, call, return, etc...)

There are more but these are the ones to come to mind. If you are starting a new project then I recommend Nios II since it has a smaller hardware footprint size and is capable of running much faster than Nios classic. Also since most Nios classic users have switched over to Nios II you can probably imagine which one is easiest to get help with in case you run into problems.