Manifold purports to be "the best GIS ever". Who am I to argue? :-) The price is certainly good. $245
I've worked with ESRI ArcView (3.x) and ArcGIS (8.x/9.x/10.x).
I like ArcMap. I will reserve further comment for a later time.
I tried GRASS and it didn't really set my world on fire.
I looked at TNTmips. I gave QGIS a shot. I've tried Delorme TOPO! and DeLorme XMap and Garmin Mapsource but they don't really qualify as GIS systems.
So I guess for me this means I have to compare it to than ArcMap.
They say it's the "most Windows" GIS but I will not hold that as a failure.
More in about two weeks...
Okay, I am back.
I spent a couple days looking at Manifold. The initial sections of the tutorial didn't make it for me, I learned 14 ways to do selections. I tried to re-do a map project in Manifold that I had done in ArcMap. Cartographic layout must be Manifold's weak point. At some later time I will take a look at its analytical capabilities.
If you must buy Manfold, go for the "enterprise" version, it's only a few dollars more than the basic version. It allows using a DBMS as a data store; otherwise all map data is pulled into the current map project. This will use massive amounts of disk space and create lots of redundancy. For example, if you have a 'streets' layer for a city and you do a series of 5 projects you will have 5 separate copies of the streets layer (plus the original). If you edit a street in project number 1, all 5 of the other copies will be out of sync.
NOTE I have NOT tested this but in theory you should be able to keep layers in a database to avoid this. Since Manifold will work with MySQL, this can be a cost-effective solution.