Prior service entertaining going back as an officer. Does any one have any insight or possible what branch might be best?

First off, you are over the age limit for the Active Army and it would require a waiver. If you continue your education, you may be able to attend ROTC during that period and commission that way, I would talk to the ROTC program at your school to see if an Age Waiver is even possible. If not, the other choice is to commission through the Army National Guard, where prior service can commission up to age 42. It would require completing either Traditional or Accelerated OCS through the Guard. You do have better control over the Branch you end up in the Guard. You would still need to attend an Active Duty Basic Officer Leadership Course for your branch.
If you go that route, talk to Officer Accessions. If you have been out for two years, you shouldn't need to repeat BCT and OCS is MOS immaterial. There are now educational and bonuses available to officers that just didn't exist in my day.

I enlisted without prior service and reported to Reception at BCT at the age of 39. But the pathway is the USAR and a Direct Commission from the "inside".

Certainly try and get the age waivers you need for the ideal path you wish, but keep in mind, Tic-Toc, Tic-Toc.

I do think your chances are good if you choose to try and get a USAR Direct Commission into an under strength branch.

A 2 Star Command in the USAR were willing (not long ago) to put up some of their budget money to fund a scholarship program for enlisted to finish college and get a commission and serve under that command for probably their first obligation period.

Now, mind you, USAR subordinate commands were not "making anything up" and handing out magic commissions. The program essentially was Green to Gold per the reg, but they were funding an expedited path without going all the way through HRC, and the catch was you basically were going to be tied to that 2-star command for a while.

While I was a 1LT Company Commander I was granting (per direction) acceptance waiver memos for candidates a few points shy on their GT score so they could submit OCS packets.

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So, what I'm saying is the path to a commission in the USAR is already greased. You're probably not going to get an Active Duty path, but then you can navigate the system by landing a full time AGR job as an officer (but just be sure you knock out your Captains Course ASAP after pinning 1LT before you do).