I would recommend a product called Cadcorp SIS, www.cadcorp.com, I have in the past used GeoMedia (which I quite Like, MapInfo, which is OK but limited and ESRI (Which has pretty a bad UI but good functionality and cost a bomb to get all the modules to do the serious stuff and link to RDBMS). I would say cadcorp SIS has the functionality of ArcInfo with all its modules and the ease of use of GeoMedia at the cost of MapInfo. I have played with Manifold which is also quite good as a general GIS tool.
It all comes down to what you want it to do. Interoprability, Editing, True 3D and Topology is probably Cadcorps strong points which is what I use and like.
Good luck with whatever you end up using