On TV Tropes, there's a concept known as the Five Man Band. This is the idea that groups of characters tend to fall into a set of well-defined character archetypes:

The Leader - the one who leads the group.
The Lancer - the second in command. Generally not as charismatic as the Leader (which is why they're not in charge) but capable enough to get things done. Often has a contrasting personality to the Leader.
The Smart Guy - the one who comes up with the ideas. Usually intelligent but lacking in direction - they need someone else to decide how to put their ideas into practice.
The Big Guy - the strong one, the one you really want on your side in a fight. Like the Smart Guy, the Big Guy is a valuable asset but often needs to be controlled or at least pointed in the right direction.
The Chick - The peacekeeper and emotional centre of the group, capable of solving problems within the group itself.

Well, you know what's coming. :) Here are my thoughts on how the Filly Five would fit into these archetypes.

The Leader - Diamond Tiara. I think she would have to be. Diamond Tiara is a born leader, and some have suggested that this is actually what her cutie mark represents. She's the dominant force in the Tiara/Spoon pairing, and Ponyville Confidential shows her leadership skills explicitly.

The Lancer - Apple Bloom. Apple Bloom is a contender for the Leader, but in the end, I think she's more suited in this role. Apple Bloom is only the de facto leader of the Cutie Mark Crusaders, and we've seen in One Bad Apple that the society is egalitarian - any one of the three can make decisions on how it is run. (This is possibly one reason they fail so often at what they're doing). She is also very much opposed in personality to Diamond Tiara, a common Lancer trait.

The Smart Guy - Silver Spoon. I have to dive into fanon for this, as it's not established in the show whether Silver Spoon is smart or not. However... she wears glasses.

The Big Guy - Scootaloo. It couldn't be anypony else. :) Scootaloo is always ready to leap into action, and is the most physical of all five fillies. In One Bad Apple, she's the one who knocks Babs Seed off the float to save her from crashing.

The Chick - Sweetie Belle. Sweetie certainly looks the part, being the most girly of all five fillies, but it's arguable as to whether she should be the Chick or the Smart Guy. I think she fits the Chick role better, however, as her intelligence is often directed at understanding and manipulating the feelings of others, particularly Rarity.

What do you reckon?

I'd reckon you're right, that setup is almost always how they're portrayed. Sweetie is definitely The Chick, since in her Canon and fanon scenes, even if she is shown as smart, she is definitely always shown as non-confrontational/peacekeeper. "Capable of solving problems within the group itself" has plenty of examples from fics and the show. One Bad Applehas her being the only one who wants to go to an adult for help, as they should have at the beginning, and fics like Serenade of Silver Belles has her pretending to be upset, just to stop a fight between Diamond and Applebloom.

Sometimes the dynamic shifts just a bit, where Scootaloo is shown as the smartest, and Silver falls to the wayside. In those situations it falls more like: Leader - Diamond, Lancer - Silver Spoon, (I know I put DT and SS as leader and second, but I can't see either as the Big Guy) Smart Guy- Scootaloo, Big Guy - Applebloom, Chick - Sweetie. Those are really the only two, to me. Even if Applebloom wants to be in charge, she really is still second to DT whether she knows it or not..

1610060 And don't forget Babs Seed is the Sixith Ranger. Hm someone should use Babs and the Filly 5 for a Power Rangers fanfic.

1610160

I was actually considering leading in to a Babs Seed/Sixth Ranger discussion. ^.^ Do we know any stories that feature the Filly Five + Babs as a six filly group?

1610185 Not yet to my knowledge. Someone should make one.

1610113

I also had Silver as a possible Lancer, because of her longstanding role as Diamond's second, but Apple Bloom just fills it so much better. :) I've not seen AB as a Big Guy, but I can see her in that role, being an earth pony, farm pony, and someone who watches their siblings kick trees all day. (Oh, and she knows kung fu!)

I'd say Scootaloo would be the smart guy.