Every med works different than others. Straterra is the only one of the three that is not a stimulant and non-habit/addictive. Metadate has been around for years (its basically ritalin) and folacin is a little different than ritalin but close. Go to this link, it is a great ADHD source. This is a direct link to drug comparisons.
http://www.addresources.org/article_adhd_medications_mandelk orn.php
bman3039063.1155671296Of the stims that you mentioned, focalin is easily tolerated too I believe...if you do a search on this medications board, you should find a lot on all three to read up on..Of the 3 meds you have listed, metadate is methylphenidate (the med in ritalin, concerta, etc) and is considered one of the first line of meds for ADHD. Focalin is the more active form of the 2 forms that make up methylphenidate and is considered "cleaner" and a good choice for those that have side effects with regular methylphenidate. These first 2 will show whether or not they work rather quickly. Strattera is more similar to antidepressants (it was originally designed as an antidepressant) and takes time to build up and become effective. Some people and docs like strattera because it is not a stimulant.
Since everyone is different, it cannot be predicted how a person will respond to any med. It is trial and error. If these 3 are not effective or show too many side effects, keep guanfacine (tenex) in the back of your mind for another non stimulant alternative or med to augment a stimulant.
Good luck with what ever treatment option you decide to go for.
Before you try medication have you done an ALCAT test to ensure you have removed all foods that are causing allergic responses as these will also cause add symptoms.
Also look at brainmakeover.com for non medication based treatment, there are many unmetioned side effects of medication!