Medication for ADHD

My son has just been diagnosed with moderately severe ADHD.  He also has high-functioning autism.  He is nearly 7.  My consultant has recommended Ritalin and I would really appreciate advice from any parent who has given it to their child.  I understand that it can cause wakefulness, lack of appetite and can also slow growth.  If the balance of opinion is that these are mild or rare, and that it improves impulse control and concentration, then I may medicate him.  But I have also been told that it can make rigidity and controlling behaviour worse in a child with autism.  Is there any other medication which is better?  I have also heard of Concerto.  Any comments or advice gratefully received.