I am in the process of applying to tenure-track assistant-professorships positions in my home country.
Some institutions request no more then 3 reference letters.
Two letters I will have from my former PhD supervisor and my current post-doc supervisor in my current institute (I am doing my post-doc at a different institute, way more prestigious then my PhD inst. and in a different country).
I have all the reasons to believe these will be very good letters.
In the past I had a third letter from a professor who knows me well from the time I did my PhD (same dept. in my home country, close topics, some collaborations over several years and very good personal relationship).
However, It was 3 years ago. He wrote me very good letters before (so I've been told and believe, I also eventually got few fellowships and had one tenure-track job interview when providing his letters).
I also have the option to ask a current collaborator from my current dept. who knows me for about a year. He is very senior and respected scientist, published hundreds of papers and was the dept. chair for many years. My work for his groups is very valuable (no one in his groups knows anything about the methods and analytical tools I use for this project of him), and we have a good personal connection.
My question is: From which one of these 2 prof. should I ask a reference letter ? In more general terms: is it better to ask someone who knows you longer and from your home country (where I also apply), or a more current collaborator from my post-doc institute who is also a "bigger name" and knows what you are working on these days?
I will be mostly happy to read answers from ones who had been in selection committees or the like, but also much value answers from others as well.
Edit: I can't simply ask from both and use alternatively, the recommendation letter should be submitted directly from them to the committee, so only one of them can be asked to submit.