that depends on the particular aspect you desire to evaluate (there are different metrics), and the particular scenario of interest.

ns-3 simulator is normally the best network simulator.

Hello,

I Think You know about simulator given below, If not then this information may be helpful to you

For 5G

1.NS-3

2. Matlab and Simulink to design, test, and prototype 5G Technology

I am sending matlab white paper for more information

For IoT

iotify

you can get more details from the link given below.

https://iotify.io/iot-network-simulator/

https://windowsreport.com/iot-simulators/

you can also look at http://www.cupcarbon.com/

1. NS-2 simulation slow for large networks

2. TOSSIM simulation it constrained to berkeley nodes

3. MATLAB mainly used for large networks

60% of the tests are based on MATLAB, followed by 28% based on NS-2.

MATLAB and NS-2 are commonly used simulation tools.

U can try COOJA simulator also but it size is very restricted

My recommendation is for you to consider NetSim https://tetcos.com/5g.html