For some pretty good information about choosing a generator take a look at 
www.nooutage.com     It has numerous area that can help you.   My wife and I have recently been looking at buying one and have done some research on it.  If you 'search' the net, you'd find even more.  One thing I will caution about....make sure you take into account the SURGE Wattage needed to start things like central AC/ Well pump etc.