I asked this once! http://www.reddit.com/r/AskHistorians/comments/1pf2a3/how_does_camel_cavalry_compare_to_horse_cavalry/

"Camels are hardier animals in general than the horse, being able to survive on sufficiently less food and water than a horse allows for a great tactical advantage, in that they can travel further on less resources than a horse. They have, as /u/LivinDavideLoca mentioned, a natural height advantage over horses by several hands giving tremendous advantages on downward swings. These benefits are offset by a few determinate factors. Horses are faster and have a straighter gait than camels; whose pacing cause a rider to sway and bob, making it difficult to train and mount archers for camels. A French Destrier is also much more resilient to physical injury than a camel is, in that it has stronger ankles and a much lower center of mass. Even a jennet has a higher work output than a camel. Camels are also significantly more stubborn than horses, they resist being moved against their will and bite, spit and kick more often."

From user TheLionHearted

While not really an answer to your question (I'm not sure of the advantages of one over the other) you might be interested to know that camels were still being used in battle in the last century: Lawrence of Arabia is perhaps the most famous example.

There's an interesting write up of one battle here, along with some photos: http://www.cliohistory.org/thomas-lawrence/akaba/

In several of the Total War games the camel units have a bonus that they scare horses due to their smell. any truth to that?