When looking at the potential candidates...here is my personal order of preference...
1. Shanahan - Has already expressed a desire to work with Tannehill, and has an offensive philosophy that would fit his skill set, he is also an individual who would do work on the offensive line, he is also a man who has worked in the league long enough to have great connection in building a staff.
2. Coughlin - For some of the same reasons I like Shanahan, also, listening to some of his players speak about him, he is someone that is well respected by his team. If you are looking for someone to make over the culture of the team, he is a great candidate.
3. Jackson - Has head coaching experience and while he didn't have success, he wasn't in the greatest position to do so, but having that experience and learning from it could help and seems to have found a way to help Dalton take the next step and may just be what we need to Tannehill. I think if he is paired with the right DC then you could potentially have the right guy.
Personally, I like the older coaches, not retreads in a sense, but those that have been around long enough to be able to sniff out bull**** quickly and make good personal decisions when it comes to who plays. I honestly have no problem with looking at Austin and Gase and think they are good viable candidates, but I just feel, based on the culture of the team and how it has gone about it business the last few season, it may need an older coach.