I know is a difficult question but some pro and cons of the main software available may help.
closed as primarily opinion-based by AJ Henderson, Paul Cezanne, Michael Clark, MikeW, mattdm Aug 16 '13 at 19:54
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Darktable is probably the current most popular option. Lightzone is another fairly recent entrant that used to be a commercial project that failed and became an open source project. Strictly on the RAW processing side, RawTherapee is also reasonably respected.
As features of each change and are updated regularly, the best bet is to download and try each and see which fits your workflow best. Particularly for workflow, the best product is the one that operates the way you work.