It's simple, free, runs smoothly, and recognized as a standard program in my country. It’s important that HEC RAS tell you where is mistake that you made. Also it’s public version and free available on HEC web site.

Hec-Ras is a User-friendly hydraulic analysis and modelling software. I have been using this for more than three years for my infrastructure projects. These hydraulics tools are great to model the 2d induction boundaries to determine the Peak flow, velocity and flood depth. The main highlights of the simulation of the final result are really cool. The simulation for any storm duration is possible. Most reliable software to analysis the peak flows and flood path. So it can determine the floodplain map, sediment transport analysis, flood control and storm drain system design and analysis.

I find it very easy. The reference and user manuals are excellent and the error reporting is also very useful in fixing errors and troubleshooting. Plus, it’s free!