tl;dr
3 positive options, 1 neutral and 1 negative, and that makes 5 in total to strike a balance. The choice of labels and emoji/smiley should target the least negative emotion and the least positive emotion; because you have to cross the minimum threshold to be in the extreme/maximum. If you are fishing for data then this is the best option. Also emotions are quite linear.
As a company that builds widgets for human emotions, I recommend you mix the principles of user experience and data from research studies to improve the product.
[SECTION A]
The University of Glasgow published a research paper last year.
Human beings are emotional creatures whose state of mind can usually
be observed through their facial expressions.
i.e. Our face is a transmitter, it transmits signals like our emotional state. In the interwebs, we use smileys and emoji to match this.
six basic emotions which are universally recognised and easily
interpreted through specific facial expressions, regardless of
language or culture. These are: happiness, sadness, fear, anger,
surprise and disgust.
Since you particularly express the state of the emotion with smiley faces, I believe this should help you narrow your options.
Our research questions the notion that human emotion communication
comprises six basic, psychologically irreducible categories. Instead
we suggest there are four basic expressions of emotion.
And the plot thickens...
In a nutshell, they built and used a Software to tell similarities in human emotions. By using these methods and techniques, they've determined that humans exhibit 4 unique emotions.
More resources linked to this research is available on this site, with a very nice video demonstration.
[RANT]
The next 2 paragraphs of this post might seem off-topic but keep up with me... I have an uncanny knack for bad examples while trying to make a point. You can skip to [SECTION B] if you wish.
Biologically, we are just like computers. So everything we have is quantifiable and can be proven to be scientifically accurate. In other words, the chances of a Mr. Anderson turning Neo IRL is questionable.
The brain processes stimuli and outputs a response based on a series of conditional statements and loops encoded in your mind. It’s doing it right now. Sensors in the medulla oblongata are gauging oxygen and carbon dioxide levels in our blood. When they reach a defined upper limit, the medulla oblongata sends signals through your nervous system to the diaphragm, lungs, and intercostal muscles, causing you to exhale and inhale. In a sense, our medulla oblongata is doing something that looks like this:
int main() {
while(alive){
if(oxygen <= 80){
inhale();
}
else if(carbon_dioxide >= 40){
exhale();
}
}
}
When a program has to interact with the real world, it uses sensors, radars, signals, and receptors. When we interact—touch, sight, body language, and linguistics are used.
Okay why did I force you to read that?! Because I wanted to introduce you to the similarities between a computer and a human. And just like computers and software, we're programmed to work/function the same. Our personality is what distinguishes us. But emotionally (i.e. visually like UI) we react the same way.
So if Human A exhibits 4 basic emotions then all humans exhibit 4 basic emotions and that's a fact.
Assuming emotions have an origin or something in common, like objects encapsulated from a class and looking at linguistic surveys... where traditionally they ask "how satisfied are you between 1 to 10" etc patterns; we can establish (for the sake of my rant) that satisfaction determines the emotion then...
would be the least possible classification. i.e. 6 basic emotions house 2 positive, 2 negative and 2 neutral emotions.
[SECTION B]
@DasBeasto is right about the Cognitive load on the user; that's what User Experience and Information Architecture is all about.
I'd argue that emotions are binary. We're either satisfied or not satisfied. Facebook took it a step further, with just "like"; reducing the cognitive load to the least possible value.
From Bret Taylor, the inventor of the Like button
I have the feeling that if there were to be a 'dislike' button is
that you would end up with these really negative social aspects to
it,” Taylor explains. “If you want to dislike something, you should
probably write a comment, because there's probably a word for what you
want to say. I'm not saying the 'like' button isn't flawed would it be
even more complex with a negative sentiment like 'dislike'.
Which is debatable, as nothing good every spawns from negativity.
But when you build a product around emotions you shouldn't focus on binary options.
