Typically, the models that include built-in decoders also are higher-line with more features. You can plug a DVD player with built-in decoder into an external decoder; you'll have to do this for DTS anyways.

Do the rest of the features included justify the added expense of the higher model for you? Then get one with a built-in decoder.

If you don't need the rest of the "bonus" features then just get a basic player without decoder.