My tenor guitar is tuned DGBd (low to high) So open G Major chord. Very easy to play chords in any key without a capo.
But main advantage for me is playing the melody in D or G is very easy without leaving first position
But you do need the correct strings for whatever tuning you are using. The 'Tenor Guitar registry' is a wonderful fund of knowledge - http://launch.groups.yahoo.com/group/tenorguitarregistry/