It depends on what country you are in and the operator that you are on because there are thousands of set-top boxes made by hundreds of companies.
Personally I am biased but I believe Humax have made some of the best boxes. They have made some mistakes but they are still a company with great integrity and good engineering.
Arris has excellent engineering, I am not sure about their software stack being as good as others but their scale is huge and their build quality is good.