Picking an advisor/supervisor is one of the most important decisions that budding young science students must make at the final year undergraduate and Ph.D level. You should pick the advisor rather than the topic. A colleague once said to me, "Students are very good at picking bad supervisors."
An important aspect to the choice is whether is better to work with an energetic young faculty member (lecturer/Assistant Professor) (a "young turk") or a well established faculty member (Professor) (an "old fart").
Here are a few random thoughts on the relative merits of each. Bear in mind these are just generalisations and ultimately you will be working with (or for) an individual human being not some abstract concept or social classification. There are always exceptions.
Young turks offer you energy and enthusiasm. They have a lot riding on your success and may have significant time to invest in you. They may be working in some exciting new area or technique. Because they are closer to you in age they may be easier to build a strong personal and working relationship. On the down side they lack experience at picking research projects, particularly ones suitable to the average student, and lack experience at supervision. They may be so desperate to succeed (survive) they may want to take more credit than they deserve for your work. If they don't have tenure they may leave in the middle of your Ph.D. Will they take you with them if they move to a different institution? You want your supervisor to help you get a job or a place in a good Ph.D program. A junior scientist may not have the necessary contacts and reputation necessary for this.
In contrast, old farts may offer you wisdom, experience, and stability. Hopefully, they have learnt from the mistakes they made when they were a young turk and are now more effective at picking good research topics, particularly ones suitable for students, and will produce publishable results in a reasonable time. They may also be able to quickly see dead ends and save you a lot of time. On the other hand, they may be stuck in a rut in an old research field and be getting distant from nuts and bolts technical details. Worse, they may have lost interest in science and just be concerned about getting grants or an invited talk in some exotic locale...
They may be so busy with travel and/or administration that you will never see them. [But there are exceptions, e.g, Glenn T. Seaborg]. They don't have much riding on your success. They have already successfully graduated students. They don't need to get tenure or get promoted. If you aren't successful or bomb, it will be more likely that you will be blamed than them. But, a positive letter of reference from them may carry great weight to their extensive international network of senior colleagues and help land your next position.
On balance, I think the ideal situation is to have both a junior and senior person involved in your research. Two possible ways this might work.
i) A junior person is your main advisor, but you regularly talk informally to a senior person for feedback on what you are doing. This requires permission from your advisor.
ii) A senior person is your main advisor, but you work closely with a junior colleague in their research group, e.g., a senior postdoc.
Again, I stress these are just broad generalisations. There will always be exceptions. e.g., junior faculty who won't invest significant time in students, and old farts who won't give appropriate credit to their students. Senior people also take jobs elsewhere and may leave you behind...
I welcome comments. Who do you think might be the best option?