It depends on who you ask, someone that only represents one brand of course will tell you the one they represent.  Ok a question, how would someone know what brand should be used?  Well this requires some reading, lets get started.

Generators used for residential or business structures are typically combustion engine driven machines.  The generator sets utilize an engine to spin a large magnet to force electrical flow.  Quality of the electrical output depends on engine speed as well as the engines response to whatever level of electrical load is attached to the generator.  For newer generators, the engine speed is controlled by use of an electronic component called a governor.  The governor controls the throttle flap which controls how much air mixes with the fuel in order to provide the correct combustion inside the engines cylinders.  How quickly the governor reacts without overdoing it is pretty important in how successful the generator will be.  Another question, there are several, what is success?  For generators of course it means the generator provides you electricity when the power company's utility source can not make it to your structure.  However success is also determined by how the generator source treats your electrical loads that attach to it.  Voltage dips or spikes are not good for most electrical loads.  A generator who's response to load attachment, whatever the level, should be stable and fast.  While there are lots of factors to this response, a manufacturer's governor platform is pretty important.

Even with a good governor, calibrations sometimes have to be made to fuel pressures, spring tensions, electronic calibrations to the governor system such as gain, stability and droop.  The only way to test all these is by attachment of an external load by an experienced, well trained technician using a load bank (external load).  To know, to see for yourself, load testing with external load is the only way to verify a generator's response to load.

Think about this, if the one you ask does not have what is necessary to safely load test or stress a generator, how could they possibly tell you what is the best brand to use?  

Okay still more, generator brands just like car manufacturers, appliance manufacturers, even food suppliers change how they provide their goods.  So just because one year a product is the best does not mean it will be next year.

Think about this, if the one you ask does not experience different manufacturer's products, stressing as needed to determine the facts, how could they possibly tell you what is the best brand to use?

There are other factors to consider, enclosures, fasteners, quality of harness connections, control platforms, on an on it goes.  The best you can do, ask someone who has worked and tested several brands, across several geoprahical areas, across several decades, in good times and bad.  Because there are so many options, ask an expert, it matters!

All structure's electrical needs can be different, an end user's needs in how they want to use their structrue during a generator event can be different.  There is really no one system fits all, there are different sizes, placement location considerations, and ways to provide load management.  Most always engine response if the most important consideration however sometimes the larger consideration is in whom provides the most practical and effective means for management.  

At E&W Electrical, LLC we represent mostly three different brands, your needs will determine which we would recommend to you.  Let us know if we can help!