Generac or Kohler is a good deal.
Better than average quality, not necessarily "good deals" !
It is hard to make a recommendation on such a small amount of information. So you want to run your sump pump. 120V/240V ? How many amps does it draw ? No lights, microwave, refrigerator, freezer or furnace ?
Do you want a portable or permanently installed standby
(Generac and Kohler are big in the standby business). Permenanetly installed ones are a lot more expensive and need natural gas or propane.
Portable means you would likely have to run extension cords to each appliance
(not really that much of a hassle if you have the cords and outages are infrequent). Or you can have a transfer switch or generator interlock
(much cheaper) installed.
IMHO the "average" home can
get by on a portable 3,000 - 3,500 watts. Of course that is no electric heating or cooling, no electric stove, no electric water heater and no electric dryer. Yes, on a well pump.
Funny thing is, many of the portable generators in the 3,000 - 5,000 are all made by the same company
(Briggs & Stratton ?), they just have different labels on them !