Which is faster operations on register operands or immediate operands?
It depends.

Like AProgrammer said, it depends on the processor.

We are in an age where there are many limiting factors based on physics in CPU construction. This means that distance traveled for an instruction and heat generated by a gate cause latency. In theory, this means that for a pipeline where the bottleneck is the decoding stage, this matters. With immediate operands, you would not need to travel to the register to grab the values, which is additional clock cycles and distance traveled. This would decrease latency, and thus increase speed.

However, in real world applications, this is very likely NOT the bottleneck, and so there will be little to no increase (if mandatory register access stages exist) in speed.