Whenever I am doing a system design, many things go into account. But if you must have an answer my current favorite box (assuming it fits all the other criteria-pattern-size-cost etc.) is the Danely SH50.
The reasons are several fold.
1: Sound quality. The detail and clarity is amazing.
2: The pattern control. It has good pattern control down to around 300Hz. This allows for greater gain before feedback because less energy is getting onto the performance area. The tight pattern also allows for a greater intelligability thoughout the room because there is less energy getting onto the walls/ceiling creating late arrivals and lowering the direct/reverberant ratio.
3: Size. It is very small when you compare the output and low freq response.
4: Arrayability. They truly array well together hard packed. This makes for a nice looking package, plus one that has even coverage across the listening area without the ever popular "swishing sound"
5: It requires only a single amp channel, so less ams and DSP are required along with less wire and install costs.
6: Low freq output. It's -3dB output is 45Hz, so in many cases you do not need a sub for full range response.
While I really like this box, I typically use them is less than 50% of my designs. The reason being that like many things, they are right (for various reasons) for a particular application.
A truly good design that works well for the customer takes into account many factors and the best solution is found for the customer.
Some of the other brands that we use in installs include the following (no particular order): JBL, Renkus Heinz, Frazier, Atlas, Community, Yamaha, Intellivox, TOA, Wharfdale, Altec, Bose, Tannoy.