The effect of methylphenidate(MPH) last for about four hours. There are many different release mechanisms in order to have the effect of one pill last for a longer period of time. I discussed APO MPH SR in a previous post. I found MPH improved my impulse control (i.e. helped me hold my tongue I might loose my temper and say something I'd later regret), but found no difference with focus (I still had no interest in doing my tax returns). It also didn't help with forgetfulness and distractability. It's other benefits are that it's the cheapest ADHD medication, it is well studied (i.e. safe), and has an effect within 1-2hr of taking the medication. Typical adult doses are 40-80mg/day. I experienced negative side-effects at 80mg/day, though I am likely more sensitive since I have Aspergers.
Dexedrine has a slightly longer effect than MPH, but still needs to use an extended-release mechanism to last throughout the day. 15mg of dexedrine costs about $1 vs. 50c for 40mg of MPH (2x APO MPH-SR @25c ea). I found 15mg of dexedrine dampened all my emotions. I wouldn't loose my temper since I wouldn't get angry. I also wouldn't laugh as loud watching my favorite comedies, and my wife noticed a negative effect on my libido (vs. MPH which seems to have made things even better in the bedroom).
Atomoxetine appears to have a very long-lasting effect (days), even though most of the drug is metabolized within 12hrs. "There was no evidence of symptoms rebound and no evidence of an acute discontinuation syndrome when discontinuing treatment." It hasn't been around as long as MPH, so it doesn't have the same safety record. My psychiatrist warned me that a very small minority of patients taking atomoxetine experienced suicidal thoughts. 40mg of atomoxetine is rather expensive at ~$3/pill. I found a noticeable improvement in my irritability (things that used to bother me didn't any more). I noticed negative sexual side-effects, so combined with the costs I decided to discontinue use.
Currently I'm not taking any ADHD medication. When I started taking atomoxetine, I had also started B12 supplements. My psychiatrist asked for a liver test before prescribing the atemoxetine, and the test results showed low B12; 229pmol/L. As B12 is sometimes referred to as the stress hormone, I've decided to boost my levels to at least 400. It seems to be helping.