Let's see this from two sides. One from your (DS) side and another from my(us applicants) side.
DS side:
Opening with multiple slots is less work for you. You will not need to review 100+ applications to find one user every time.
My side (us applicants):
Being with ChipMixer will be a next level of experience.
Not sure about others but when I see an opening for ChipMixer I feel excitement with thinking that YES this time I am going to make it! And so far no luck. Sometimes I feel bad for myself not to identify the ingredients that I am missing to be accepted. This feeling of excitement and ending with bad emotion is something that can not be realized if you do not experience it. I kinda like it. So from my side opening for a single slot is much more fun although it's more work for you.
Summary:
If you want less hassle then go for an opening with multiple slots and if you want us to feel the excitement of having an opening slot then go with one single slot every-time whenever available. :-D
You could just as easily argue the opposite. Having several slots open up is arguably more exciting than just the one. The likelihood of a user being the chosen one out of all the participants is very low and you'll roughly get the same amount of applicants whether there's one slot or several so the more slots the better the odds and the more chance of you having a slot. It just makes it fairer and easier on Darkstar as well as there's always going to be several worthwhile candidates and it's easier to chose a shortlist rather than just the one.