Not to be rude, (I know people who say that are usually rude! LOL) but if you don't know electricity or generators you'd be money ahead to pay someone to figure it out for you.
Will the generator run full time, part time, or just as an emergency generator?
How large is the load going to be? How much of that load is inductive vs. resistive, (motors starting, motors running, lights, heaters, etc.)
If it's an emergency generator, how much of your household load do you really need to power? Does it need to be auto connect vs. manual?
For example, I live remote and off the grid. I have a low rpm diesel high end generator. Auto start, auto connect. Expensive and will last for years.
I have friends who just want to have some heat if its winter and keep the food in their fridge, freezers safe. I've helped them wire their furnace so it plugs into the wall. Had them buy a good, (but relatively cheap) small high rpm gas generator. A little 2kW honda generator to be exact. Weighs about 50 lbs. Told them to keep it in the house where its warm. When the power goes out start it up, pack it outside and run a extension cord into the house. And plug in the furnace, freezers, etc. as needed. No big, expensive generator sets, transfer switches, or wiring job.
And I haven't even touched on electrical code issues. Or the trouble it could cause you if the install isn't code compliant and something happens.
And in my opinion brand is critically important. What good is a generator if it's hard to start? Doesn't like starting when its cold? Load regulation is **** so when a motor starts your electronics go ****?
Hire someone you trust and let them figure it out.