There will always be debates on what exercise is better for whatever purpose and people will die on a hill for one or the other. Some debates have valid points for both and can have an intellectual argument with no malice or personal agendas but others however; argue with such childish tendencies and make it sound like an 11 year old having the argument of why "my dad can beat your dad" and throw stupid derogatory words out and throwing a temper tantrum thinking he's right and superior. It's sad when people act like that.
When it comes to these specific exercises, they both have their pros and cons yet both work very well whether one or the other and together as a team. Why really argue and try to avoid one like the plague? Unless you have some sort of crazy injury, you can adapt to either one and both have multiple variations that potentially work for anyone. It's a matter of what you're going after. Fitness is about the journey and some days you'll want to do one or the other, sometimes you'll want to do both, you're still ahead of the curve.
Although I'm more of a fan of the Step Ups, I don't really replace them with squats, it's a preference actually. Squats are essential to the development of the legs and high rep work has it's value but it's not the king of all schemes, nothing is. Personally, my favorite variations of the Squat is Hindu Style, Goblet Style & Wall Sits (+ Their Variations). Doing hundreds of reps of either one comes in different formats, done both of them with a countdown method, with decks of cards and in a row. Keep things fresh and exciting to want to come back for more. Years ago, I would start with 500 Hindu Squats and move onto to a circuit or isometrics or even start a day of activities, when I would do 500 or more Step Ups, I would just chill out or find other things to do after.
I've made points in the past why at times I left the squats to focus more on step ups but these days at least in the last couple years, I've slowly transitioned to doing both in different ways and making it work in my favor. With the Squats, I'm a lot more methodical then I used to be, I was more about speed and how fast I can do certain numbers in a certain timeframe. That bit me in the ass a couple times and it was a good lesson to learn. Now, it's a more natural pace, not going so slow that it looks like I'm breaking Snail Speed but also not going so fast it makes Sonic look like a slow poke. Building a rhythm.
Step Ups have really been the same style of pacing and it works for me, not doing it to make squats look obsolete that's not it at all, I do it for the enjoyment and what it does for my legs. Work with what's best for you, no one else, if you prefer squats more than step ups, that's great and I want you to be successful at it, let people enjoy what gives them benefits and the challenges they can do to overcome whatever. Arguing in a negative way doesn't actually help or inspire anybody. Said it before, they have good and bad points but it's up to the individual to what they gain from either one.
You are only one person, train your legs for whatever goals you have and find the benefits in them while minimizing or reducing injuries as best as you can. Be amazingly awesome and go kill it with your leg training, don't forget to still be able to walk out with energy in the tank.
