ICEMCFD is very good software for automatic mesh generation and exporting mesh to other softwares. But it has not more capabilities for gometry creation and editing. Also it has not many tools for mesh editing. CFD packages need a software such as PATRAN. It is the best preprocessor for FEM packages.
Gambit has geometry tools, but they are very limited and you don't have any tools for mesh editing. Real and Virtual concept in GAMBIT are not a professional concepts. Some tools work with Real objects and some with Virtual objects. In gambit you can not apply boundary condition on a grid face, instead you should have a surface for this purpose.
I believe STAR-CD has better concept. Because you can work with faces and nodes. But mesh generation and editing is very hard and sometime it is impossible. In fact STAR-CD does not have any geometry objects such as surface and solid. I believe Prostar is not a real preprocessor.
If these softwares combine together we get a good preprocessor