For the features packed into the 596 HD DI, it's a great choice. I get great reviews back on it, and sell a lot of them at Bass Pro. However, my own recommendation is to consider the 597ci HD DI, which has GPS for just a little bit more (like $80). The ability to mark structure on the DI is very beneficial.
As far as what floatman was saying, the 788 ci is a great unit as well (I own one), but the features in the 788ci HD DI are not worth the extra $150 over the 597 if you don't plan on using the add-on's or the Ethernet connection. Hope this helps!
-Matt