Order of authors for a tenure-track assistant professor in the USA: second author after Ph.D. student or last author? I am a second-year Assistant Professor in an engineering department at a US university. I did my Ph.D. in a non-US university and post-docs in the USA. I have a two papers that my Ph.D. students are about to submit, with 5 and 7 authors respectively. A Ph.D. student of mine will be first author in each of those, since he contributed the most, no doubt whatsoever with this. 

But what is best for me? I am definitely the person who contributed the most after my student. I had always assumed that I should be the second author. A colleague in Europe told me, however, "Are you crazy? You should be the last author of the list, which is the most prestigious spot after the first author! The main PI or person who helped most the student is always the last author in the list!" So now I am doubting my choice. 

Where should my name be on the list, given that I am the main PI and I helped the most? I know it is surely not the main factor for tenure, but I'd like to do this in the most correct way.
The answer for appropriate author order is very dependent on the culture of your (sub)field.  For example, if you are a computer engineer, you should probably be second author, while if you are a biological engineer, you should probably be last author.  Follow whatever you see others doing in the venues where you are submitting.

That said, these days it is often possible to make the contributions explicit so that there are no questions about contribution.  Many journals now request or require an "author contributions" section that attributes specific work to specific authors. Even if the venue that you are submitting to does not have such a requirement, you can still  add that information into the acknowledgements section.  Furthermore, the CRediT taxonomy provides a set of standard widely-recognized roles that are useful for describing such work.