What do you see as the pros and cons of each? 
Well... all of them are quite close to both school and home.
Huxtaburger seems like a really chill place and is holding a "trial" shift which is a pro. For the others
Grill'd:Pros:
- The employees seem incredibly nice and are really friendly
- Paid sick and holiday leave
- 50% of burgers (how could that not be a pro?)
- certificate 3 in hospitality through a training program with William Angliss
- Super flexible with exams
- Manager is super chill
Cons:
- Not many extra employee perks like maccas for say
- Having to walk across Yarra bridge (don't know what it's called but it smells) and walking through some blind spots at night
- No pay rise until the completion of the hospitality course (10 months)
- No penalty rates
Maccas:Pros:
- 50% of McDonald's and that perks card with other places
- Great international reputation for future resumes
- Incredibly familiar with the menu, restaurant, and procedures
Cons:
- SUPER busy and a commonplace for night time fights (hence it'll be stressful and chaotic)
- Not many shifts (from what I've heard)
- Heard that Maccas apparently makes people work overtime
- Shitty pay
Huxtaburger:Pros:
- Really chill and friendly place
- Can do whatever job whenever (no fixed positions)
- Pay is pretty good for starters (I think)
- Shorter shifts (3 hrs per shift)
- Paid sick and annual leave
- The manager is super nice
- Flexible around school and exam periods
Cons:
- Mirrors everywhere (I hate mirrors)
- Would become the youngest employee