It's a Chevy vs. Ford argument. It is whatever brand you prefer that is the best for you. Some have said that Colt has better consistency in thier product, while others have said they have seen numerous QC problems with Colt. Some have seen many problems with Bushmaster, while others have gone through a number of them with absolutely no problems whatsoever.
Every company puts out lemons. Sometimes it has to do with the assembly, sometimes the QC, and sometimes there are faults with the parts that can't be seen until they break. As with anything mechanical, it can fail, but it is the luck of the draw that can determine if you have a winner or not. If your rifle functions flawlessly for you, then it is a good rifle.
Many times it is abuse that will determine a truly quaility product. If you don't abuse your rifle and it has functioned flawlessly, it will probably continue to do so. If you want to put it to the test, take a tactical shooting class with it and see how it fares. A good range test is to dump four or five thirty round mags through it and see if it chokes or not. If it can do that, then take it to a class and see if it can take some more punishment.