It's not really possible to give advice on this without more information. Which sets are you speaking of, exactly? Many times the train manufacturers will make different versions of similar sets, and in different product lines. Some are more expensive than others. Also, they may make the same set in different years, except with different features.
Without some additional identification of the sets you're considering, it's impossible to make any comparison. Confusing, I know, but it's a bit like asking someone to compare a Chevy Malibu and a Ford Taurus. You can't do it without more specific information.
