The Trio of Di'angelo is the set of Di'angelos from each series. The Original with the line eyes from the original show and the two newer versions with the circle eyes Negative and Positive Di'angelos from Di'angelo: the Animated Series and Di'angelo and Aza.
Di'angelo or OD is just a plain version of the Di'angelos. He has a lazy and/or calm personality (unlike the other two) often not wanting to do anything but lay around all day and play video games. He's a little less anthropomorphic than ND and PD (like him almost always walking around on all fours making him more quadrupedal than bipedal).
More about Original Di'angelo Di'angelo (character).
ND makes you cringe when you think about him. He has a (like his name) negative attitude and very mischeivous and descructive in his matter. He often loves for crazy things to happen due to his overhyperactive personality. He loves do hazardous things to happen also for fun or when he's bored. He, however, being slighty twisted in the head, is somewhat responsible and will help his friends if they're in trouble.
More about Negative Di'angelo Di'angelo (Di'angelo: the Animated Series).
PD has a 'positive' attitude. He's very loving and caring. He has a shy personality and doesn't really care for a lot of attention from others. He always worries about the feelings of his friends and family (especially Aza). PD is often the middle man for things and will have to solve whatever surreal problem him and his friends are in at the moment. He can be extremely emotional at times (often even breaking down into crying sometimes). He also getting scared and/or confused pretty easily. The only two things he shares with ND is their look and their hyperactiveness (even though PD's is a little calmer than ND's).
More about Positive Di'angelo Di'angelo (Di'angelo and Aza).