30mm snap clips - great for barely there hair.  This clip has the best hold for thin hair but does not hold very much.  This clip is usually chosen for babies with hair just growing in where the bow is more of a decoration or children with super thin hair.

1 3/4" Single Prong Alligator Clips - These clips are partially lined to allow them to easily be slide into the hair.  They are available with or without extra grip and can serve to pull the hair back from the face.  If you are putting bows in front of a pony tail this would be the perfect clip to easily slide in.

1 3/4" Double Prong Fully Lined Alligator Clips-  These clips have the next best hold to the snap clips.  They are available with or without extra grip.  The ribbon lines the entire clip giving it a nice look and a better hold than the partially lined clip.  The disadvantage is they are harder to slide into the hair.

1.5" or 2" French Barrettes - These are my favorite clips for my daughter since she was about 3.  They don't fall out but you do need to have enough hair available to fill the clip.  They stay put pretty much however they are used as long as there is enough hair to fill the clip and make it tight.