The most frequently recorded of the major compositions of Berlioz is his Symphonie Fantastique, but Harold in Italy, not quite a Viola concerto, although giving that instrument many passages of beauty and excitement, has comparable attractions.
Of the dozen or so recordings of it which I've listened to, I'd suggest the thrilling performance led by Charles Munch with the Boston Symphony for anyone who doesn't currently have this in their collection. High-powered performances of four Berlioz overtures are also included, making for a superb overall Berlioz collection. This was selected for remastering for SACD in the "Living Stereo" series and the compatible disc also has an excellent quality CD layer. Available here
from several Amazon sellers at typically bargain prices.