This site has a lot of good info about generators, though his recommendations on generator size are grossly underestimated. http://www.generatorjoe.net/page.asp?id=20
I used a 2000W inverter-design generator in the past to power essential circuits in my home, but it required me to actively manage what circuits got power when.
The 4500W generator I have now easily runs all the essentials without having to worry about switching circuits on-and-off to avoid overload.
If you have to deal with electric heat, hot water, oven or air conditioning you will need a larger generator. But larger generators burn more fuel per watt produced than smaller.
Electric start generators are nice, but if you don't maintain the battery on a trickle-charger they are no more convenient than a recoil-start-only generator and a lot more expensive.
If you have natural gas and can afford a permanently-installed standby generator, that is the cheapest fuel to burn and requires the least amount of maintenance. Propane is also easier to maintain than gasoline (or diesel) but no less expensive (at today's prices); but if you already have a 500+ pound propane tank it might be worth considering. Diesel fuel is a little less expensive than gasoline, but it doesn't balance out the higher cost of the diesel generator unless you use it a lot.
Inverter-based generators such as available from Honda, Yamaha, Hyundai and a slew of Chinese clones of Honda are safer for electronics, quieter and more fuel-efficient. However most modern generators are well regulated, and most modern electronics are tolerant of less than ideal power supplies. I have a shit-load of electronics at home including a full electronics design/build/repair bench and have never had anything balk at the juice my $300/4500W generator puts out.
If you want to wire the generator into your home electrical system the generator will need to have a 220V receptacle. You will also need the correct 220V locking MALE receptacle, generator power cord and either a transfer switch or mechanical main/generator interlock device. Backfeeding your load center via a drier or oven outlet is very dangerous and should not be done.