Me and my team want to make and RPG but we can't agree about the camera style. We are 6 people and 3 want 3rd person and 3 want diablo style. Maybe its a problem with my team and we don't share the same perspective about this game but my question is: What is the best camera style for a RPG that want to highlight the STORY of the game? And another question: Do the player have any preferences about the camera?

The camera setups are very similar (both are 3rd person camera), what differs is control. Point'n'click vs WASD with either fixed, free or shoulder attached 3rd person camera.

You can deliver an interesting story with both approaches, what is more important is the level of immersion. Immersion depends on a lot of factors, camera is only one. In my opinion the level of immersion decreases with following camera setups:

1. FPS camera (best)

2. shoulder attached third person

3. free third person

But it only matters if your story elements are equally embedded in an immersive world. If you only have some text, cut scenes, dialogs, the camera doesnt matter much at all in my opinion. In this case it would be more important to setup the camera to support the game play.

Someone told me that the fps camera in rpg create some unpleasant things for a small indie team. In this case you must have more detailed graphics for world and character. But if the camera is like in Diablo 3 we can cheat a bit and make our job easier by making the models faster.

We have more than text, cutscenes and dialogs. We want to make a rpg like path of exile, torchlight, even skyrim.

We won't be similar to diablo. Do the average players have any preferences about camera? If we will let the player control the camera (free camera)?

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Personally, just as an "average gamer", I'm fairly ambivalent about the camera as long as it's smooth and not frustrating. If I feel like I'm constantly fighting with it, or if it's awkwardly colliding with things, it kills my desire to continue playing rather quickly. Diablo III, if I recall (it's been a few years) was rather convenient because there was no need to control it which left the player free to concentrate on playing the game. However, if that was implemented poorly, I think it would have frustrated me. It worked because generally, it gave a large enough view to not merit needing to rotate it, walls were clipped to avoid hiding the player and enemies, etc.

But, since you're really asking about two different approaches to a 3rd person camera, what it seems you're asking is how much control to offer the player. So, this rests entirely on your ability to offer a reason to allow or restrict the view. I personally don't think either approach is better or worse as long as you use that perspective to make life easier for the player. I.e. if you allow rotating the camera, make sure your collision check isn't annoying, or that there isn't wall clipping blocking enemies/player, controls are smooth, etc. But, if you're not offering any benefit or reason for rotating the camera, it's just one more thing for the player to handle, and one more thing to get in the way of gameplay.

Alternatively, you could use the 3rd person camera to your advantage to limit perspective, to make the player worry about what's behind them, out of view. Which, if done right could be a fun thing, if done poorly could just be annoying

Either way, neither approach should affect your story I wouldn't think. I don't think either way is more immersive either(as they're both technically 3rd person cameras). I don't think either approach will make you look like a "clone" on its own, as there are countless examples of dungeon crawlers with that camera perspective. You'll simply just fall into that genre, the way FPS shooters aren't all called clones of any particular game(well, sometimes they are, but not simply because they use an FPS perspective :P).