The BBC ran an article in 2008 about Flat racing vs National Hunt racing. They asked the two leading jockeys from each sport respectively to give their opinions:

http://news.bbc.co.uk/sport1/hi/other_sports/horse_racing/7436301.stm

Love The Races also ran a similar article  called Flat vs Jumps:

http://www.lovetheraces.com/features/flat-vs-jumps/

"Good jumpers: Jumpers come from a variety of backgrounds but are traditionally more robust types, bred to start over small jumps (hurdles) and eventually graduating to the larger steeplechase fences. They are generally expected to peak from between seven and 10 years of age and compete over longer distances, starting from two miles but stretching as far as four and a half miles in races such as the Grand National at Aintree (Saturday 6th April). As they tend to carry on for longer than Flat horses, jumpers are invariably neutered (or gelded) to keep their minds on the job in hand."

"Flat horses: Flat racing, on the other hand, is for a sharper, more precocious individual and they begin their racing careers at the age of two. There is more prestige on the Flat and the very best, like a Derby winner, become so valuable they can be retired for breeding as early as at three years of age. These horses can earn up to £100,000-a-time for coverings (matings)! It's even been estimated that the great Frankel could command a fee at stud of a whopping £200,000! Speed is of the essence, with the shortest races held at five furlongs (1km), but many will run over further than two miles and can also try their hand at jumping."