Open source GIS and R

Dear list members,

I am an ecologist interested in spatial and landscape ecology and a user 
of ArcView 3.3 with little experience in ArcGis but I would like to 
migrate to an open source GIS with an interface with R.
I know that there are several options: QGIS, SAGA, GRASS, Illwis.

What will be the best option of these or other alternatives?

Best,

Manuel

Manuel Sp?nola, Ph.D.
Instituto Internacional en Conservaci?n y Manejo de Vida Silvestre
Universidad Nacional
Apartado 1350-3000
Heredia
COSTA RICA
mspinola at una.ac.cr
mspinola10 at gmail.com
Tel?fono: (506) 2277-3598
Fax: (506) 2237-7036