Not necessarily. A single din can have better features than a double din and vise versa. Though you can only fit so much stuff in a single din where it becomes crowded and then double din takes the lead. If you're talking about sound quality, then it comes down to what features it has. Make sure to get something that's atleast 4v preouts and has a high quality 24 bit DAC.
Most of the time double din is significantly more expensive and that's because it's jam packed with features. It's more of a visual thing than anything. A LCD screen will cost more, touch screen, DVD player, navigation, etc.. You can find bluetooth features on both single and double so that's not a problem. I personally like double dins because of ease of navigation through my music, navigation, the ability to play dvd's. You can find a lot of the same great tuning features in single dins like Crossover points, Multi band EQ, 3 way active capabilities, time correction, etc..
Really comes down to what you're looking for in a head unit and what you can afford.