We have a 4500 watt (peak, 4,000 continuous) Honda super quiet and those last two words made it expensive, about $2,500. It's in a foam-lined cabinet and has what looks like an automotive muffler on it. I forget the sound level but you can stand next to it and carry on a conversation without raising your voice. I paid for that so if I ran it at night I didn't want to have the neighbors coming after us with torches and pitchforks. And we'd like to get some sleep too.
Before buying it I did a lot of reading about using generators to power a home. Back then (~1999) whole house generators usually started about five figures.
In our old house the power lines were up in the trees and we were virtually guaranteed to lose power in a thunderstorm about half the time so it did see use there. And yes, we did have a transfer switch to isolate the house from the power lines during use. It will power a gas furnace (just the blower motor, really to think about there) the refrigerator, TV, computer and a few light bulbs. It will not power a central air conditioner, or at least not the start-up power a CAC needs. and if we wanted to use a high-draw appliance like a hair dryer, microwave, or clothes iron you need to know what wattage or amperes they need and start load shedding so as not to overload the generator. And you also need to know what leg each load is on so you don't leave one leg unloaded and overload the other. If the circuit breaker on the generator only looks at the whole load you can still fry a winding in the generator.
A couple of other things to think about with a portable. If you're thinking about using it during or shortly after a storm while it is still raining, you'll need to put it under a roof that is not attached to your house so the attached garage is out. One may exist that is weatherproofed but I never found one and I looked. If in an attached garage it will take a while longer for the carbon monoxide to get inside, but it will eventually and it will kill you and your family. If you don't cover it and keep it dry you risk electrocution by simply walking near it to add fuel or shut it down when the power comes back on. Permanent installations are weather-proofed and properly grounded so don't have those issues.
Permanent installations have come down in price but a lot depends on the installation. If it runs on natural gas you'll need to run a gas line of course and if propane you'll need a large tank for that. Also, if NG, does the supply to your house have the capacity to supply the generator or will you need to enlarge that too?
Also, do you want to be able to run everything in the house, or are you willing to have only partial power to selected appliances/outlets to get a lower priced generator and installation?
Here's a link to a
page of whole-house generators at Home Depot. On that page alone they range in price from $1,861 to $16,000 depending on capacity. They've come down a lot in price since I last looked! An item to look for carefully is the noise level and to do some reading on what that number means. If the manufacturer made any effort to keep it quiet (and this will matter a lot!) they will proudly say so and what the noise level is in their advertising. If you can't find the noise information it is safe to assume it's noisy as h*ll and as 2B pointed out it is annoying to the neighbors. In a prolonged outtage you're gonna have the neighbors hating you for that.