All the equations and numerical methods, and source code from the 2D flood model (MOHID) is available online. This is a collaborative, free, opensource “model.” HEC-RAS is free, but not open-source which means that an advanced user is not able to check source code or modify it.
FLOOD numerical solver (MOHID) was analyzed for comparison with a benchmark study from UK Environment Agency. This methodology has been adopted as the world reference for benchmarking 2D flood modeling. FLOOD results are compatible with most solutions.
FLOOD can be used as a single tool for an integrated 2D flood model, while HEC-RAS does not have direct rain-on-grid, infiltration, or evapotranspiration. You would need an additional tool called HEC-HMS for other hydrological parameters and processes.
You do not need to specify the area or time of concentration for a catchment in FLOOD. Digital Surface model together with 2D calculation (Saint-Venant and Manning-Strickler equations) will do this for you. Additionally, you do not need to enter depression data as the 2D surface contains topographical data which is considered in runoff estimation. FLOOD has tools to remove depressions from the ground surface if required.
FLOOD is a full GIS-enabled GUI. You can handle GIS data inside (e.g. Bing Maps; shapefiles, RASTER files, etc.), including results visualization. HEC-RAS visualization needs to be handled in separate tools or 3rd party software licensing (e.g. such as ArcGIS).