Hard question to answer because there are so many different factors to consider. Whilst my opinion is biased towards Adelaide, I will try and be as objective as possible.
Cal &
Dreamer &
Yamster are UQ dent students who can definitely give their respective insights for you.
Course Program Differences
Both degrees are 5 years in duration.
University of Adelaide's dental program is entirely integrated meaning that rather than having 4 different subjects/units, it is all combined into one. This is typically done through Integrated Learning Activities (ILA or PBLs) which helps to contextualise everything that you learn in lectures, sim clinic, clinic and workshops into a dentist/dental-assistant/patient context. Personally, the lecturers who teach the dental-related content are extremely good at their field but the ones who teach biology-related foundational content can vary greatly at times. With regards to the recent outbreak of COVID-19, our coordinators have worked marvels in making the transition for us as smooth as possible despite the recent set of events -> can definitely vouch for my dental school being very adaptable when it comes to making course amendments on the brim.
Definitely need some more clarity on this one but UQ's program is an embedded honours right from the start which could definitely play a factor if you are interested in specialty programs (although Adelaide uni also has options for honours as well if you are able to maintain great grades).
Rankings
Rankings are generally not reliable indicators of uni performance. UAdel & UQ are both highly-reputable universities for dentistry and as such, this should not be a major factor when it comes to choosing your school. In fact, any dental school that is accredited by the Australian Dental Council are great options. You ultimately graduate as a dentist in the end.
Vibes
Generally, Adelaide's vibe is generally much calmer compared to Brisbane. In addition, the weather here in Adelaide is much cooler in temperatures compared to Brisbane. The parklands here around Adelaide are plentiful and really gives off a great vibe especially after a busy uni day (not that I have been to uni that often ever since f2f classes). With regards to costs of living, both cities are generally pretty similar -> it mainly depends on you personally and what your spending priorities are when it comes to your daily lifestyle. In addition, UAdel as a Go8 university has a relatively smaller campus which is more lacking in extracurricular activities, sports & clubs in general when compared to UQ. Whilst most of the major stores are available here in Adelaide, a major minus here is the absence of stores like Uniqlo and 7/11 (as examples) which are otherwise present in Brisbane. However, Adelaide uni is sooooo close to Rundle Mall which is houses almost every big store that you can think of.
Both Adelaide and UQ have up-to-date sim clinics with modernised tech, x-rays, etc.
However... SA has generally been one of the best states to be in when it comes to being safe from COVID-19. Also, Adelaide has the super cool-looking AHMS building with the Adelaide Dental Hospital on the top few levels. Say less.
Final Summation
These are just some ideas that I came off the top of my head with. Definitely not an exhaustive list. Main points to consider are whereabouts you live in (which place is closer or further to you), what vibes more with your preferences, climate atmosphere, preferences for integrated course and just sorta what kind of views you want to experience or be a part of in your journey.