I've played both, and although personally I prefer paragon as I always opt for the 'good' moral choices, I think ME is one of the few games in which the 'evil' moral choices are well implemented. In many games, the 'evil' choices tend to come in the form of general asshole behaviour for which the only motivation seems to be 'because I like to be a dick'. Evil for evils sake, in other words. However, the renegade choices in ME have always generally been justifiable, and fit in just as well with the story as the paragon options.