I don't have much time to type now so will keep it short, It depends on what your needs are, the most popular options are the 3KW (really more like a civilian 4-4.5 industrial model) MEP-016 family, these include the older gasoline powered pull start MEP-016a, and c, the 1980's Onan diesel powered electric start only MEP-016b, and the 21st century Yanmar retrofit diesels, the MEP-016D (a or c retrofitted with Yanmar L70 engine) or MEP-016E (b with Yanmar L100 engine) The yanmars have the advantage of being both pull and electric start. There is also the MEP-701 which is a 16B in an ASK housing. All of these are 3600 rpm screamers
Then at 5KW you have the MEP-002a, this is a MUCH larger unit than the MEP-016 family as it is powered by a 2 cylinder 1800 rpm diesel egine
and at 10 KW you have the MEP-003a also an 1800 rpm, but powered by a 4 cylinder diesel. (both are again under rated by the military as those 5 and 10 KW ratings are 24/7/365 in nearly any conditions on the planet)
In addition to these we are just starting to see the TQG series show up on the surplus market, although they are still rare, and priced fairly high.
Ike
p.s. remember in general the larger the generator the more fuel it will use, for minimalist survival in a mostly gas house a 3KW MEP-016 family unit can work fine for winter outages, it can generally keep a refrigerator and chest freezer running, as well as run up to a 15 amp furnace blower, a variety of modern CF lights, as well as tv, computer, etc. Or for summer outages you can substitute 2 small, or maybe 1 small and 1 medium modern window air conditioners