We will not judge the aesthetic factor, as purely subjective. Important features when picking a case that should be considered are:
The build quality is also very important, and it is better to still prefer aluminum to plastic cases. Unfortunately it is not easy to evaluate and in many cases you just have to trust the reviews.
Among our favorites there are the Corsair 4000 and 5000 series and the Fractal Design Torrent series, with various models covered in all price ranges. Good alternatives in high-end mid-tower are the be quiet! or the Cooler Master. If you have enough space, you can opt for a full tower.