I voted for iGO as my favourite.

I usually have OziExplorer running as well as iGO, using the Ozi Screen Designer makes it very customisable by designing your own screens however you want them.
Converted some vector maps to raster of my local area & made them with a black ground colour/background for using at night time, a lot easier on the eyes at night than the lighter coloured Geo maps.
All up it's a pretty good program.

I find iGO8 suits me better than Primo, it's a lot easier to create POI's, place pins & change screen zoom levels on-the-fly than Primo is.
Primo will read & display pins from iGO8 but it won't allow creating of new pins, well not that I can find anyway.
AFAIK Primo's zoom can only be changed in the map settings, iGO8 it can be easily changed by just tapping the screen to bring up the zoom controls, where 3 or 4 different zoom levels can be set.
And there's a few other little differences iGO8 has that they removed from Primo that I can't think of at the moment that makes me prefer iGO8 over Primo.