The answer with all questions of this manner is "It Depends". Specifically, the factors that influence the decision are:
- Are you competing in a strength sport? If so:
- How close to the contest date are you?
- Is the squat a contested lift (usually only Powerlifting, but occasionally this applies to Strongman as well)
- Your individual lever lengths and insertion points. Everyone's skeletal structure differs in subtle ways, and where muscles attach to the skeleton also differs in subtle ways.
- Your comfort level with any particular type of squat
- Your training maturity
- Personal preference
In all honesty, unless squats are a contested lift they really aren't even a required exercise. However, they are an excellent full body exercise that help build mass and strength overall. I know of several weightlifters and strongmen who squat routinely even though it isn't a contest lift because it has good carry over to the events they actually do compete in.
Taking a survey of some of the top powerlifters (the only sport to consistently include the squat as a contest lift) you'll find that training styles vary across all of them.
- Bulgarian and Russian training favored always training the contest lift.
- Westside style training (geared lifters) favored training other lifts to build up weak areas.
- Several Raw lifters train variations when they are pretty far from a contest date, and then specialize in the contest lift when they are closer to the contest date.
- Chinese weightlifters are known for hitting accessory lifts hard and doing something that resembles "powerbuilding" (hybrid of powerlifting and bodybuilding).
Pick one style and make the most of it.
At this stage in your training career you are focused on just getting stronger. It's less important whether you choose wide stance or narrow stance, and more important that you consistently improve as the bar gets heavier.
- Achieve depth: crease of the hips below the tops of the knees (or better if you can)
- Balance: keep the weight of the bar over mid foot
- Chest up: keep from folding over like an accordian (and it assists with point 2)
Beyond that your personal squat style is your personal squat style. Embrace it and get stronger at it. Subtle changes can lead to feeling substantially stronger and more stable under the bar. Those are the types of adjustments you'll want to make. Pursue better, ignore what everyone tells you is "best" or "optimal" since those are things that are impossible for anyone to truly know. Not to mention, "best" and "optimal" change as you get stronger. Just pursue better.
Intermediate to Advanced
Use different variations to fix weaknesses and to avoid boredom.
This is where the arguments of using squat variations really come to play. Several variations have a different training effect:
- High bar vs. low bar: high bar lets you set up with a slightly more upright back position. It's less punishing on the lower back so it's good for a general strength builder. Low bar lets you push a more weight due to changes in leverages, but is harder on the lower back.
- Wide stance vs. narrow stance: One of these will feel stronger and more natural to you. Using the opposite stance will hit muscles differently. Wider stance will involve more adductors and narrower stance will help you get more of a rebound out of the bottom.
- Paused Squats: Paused squats take away the stretch reflex and force you to work harder to get out of the bottom. They are very useful if you are fixing squat problems, or you just need to build more strength coming out of the hole. Another variation is breathing paused squats where you release your valsalva while at the bottom and pause for a couple breaths before coming back up. Be sure to reduce weight when you perform these variations.
- Box Squats and Partial Squats: These are special purpose tools to address certain goals. You can work with more weight using partial squats, so some bodybuilders use them to build more quadriceps mass and some sprinters will use them to build more quadriceps strength. Box squats can be used like pause squats, but they are more favored by geared powerlifters due to the way they have to load the squat suit.
- Split squats, lunges, single leg work: These are useful to sort out discrepancies in strength between your right and left leg. When using both legs together, the proportion that each leg contributes to the squat doesn't change. However, when you work one leg at a time you can fix that to a certain degree.
The bottom line is that as you mature as a lifter, you'll pick your squat based on what you are trying to emphasize at the time. And some people are just fine doing nothing but one kind of squat and get stronger. There are no hard and fast rules, only guidelines.
I personally use more variation when I'm in my off season, favoring the variations that are harder for me to perform. As I get within 2-3 months of a competition, I focus primarily on the events in that competition.