US domestic connections are generally a piece of cake. At most 'hubs' you never have to leave the secure area and often the gates are close to each other.
One bit of advice is to book a longer connecting time than the so-called 'best' one; - gives you a bit of leeway for delays etc. Anything under 4 hours is still a legal connection and often (but not always) a bit cheaper too.
Atlanta is an easy hub, assuming no thunderstorms
. Personally I avoid Denver, Chicago ORD and New York (JFK) due to both weather and layout.