What was your experience going from 12B to 12A? Was it worth it? Any regrets?

You don't actually get to pick your MOS when you commission through Green to Gold. You could just as easily be a transportation branch officer

I was an 11B that ended up a 12A. I was already scheduled to go to PLDC to promote to E-5 when I chose OCS instead, so I was E-4. I enlisted Infantry and Commissioned Infantry, Branch transferred to the Engineers when I moved to Kentucky and the KYARNG at their request.
Are you trying to decide about the lifestyle? If you like the interaction at Squad and Platoon level, enjoy the camaraderie of the Squad, and like being an NCO., you will lose most of that when you commission. While I had good relationships with my Plt. Sgt's and Squad Leaders, you will never have that feeling of belonging again. At Company level, which will generally be the highlight of your career, you will end up being closer to your 1st Sgt. than any of your officers just because you not only have to train them, you have to evaluate and make decisions that can seriously effect their futures.
That said, I generally liked my Platoon time and Company Commander and Assistant Brigade Engineer were the two best jobs I had in the Army.
Be aware that going Green to Gold is an ROTC program and while you do get a preference list, your branch choice is Needs of the Army. While there is generally the opportunity to Branch Transfer when you hit O-3. that isn't a guarantee and you can end up a Supply Officer (which isn't bad for your career, BTW).

Started as a 12B, commissioned as a 12A through Green-to-Gold.
The obvious benefit is the significant pay increase you'll receive that will help you and your family achieve more financial independence, but at the cost of time. Being an officer you'll spend more time being in an office; planning, resourcing, creating products, and managing. So I always tell my Soldiers that they shouldn't let the pay be the deciding factor when deciding on a commission.

I chose to commission because of the level of impact that I could have on the Soldiers whom I serve. As a Team Leader I had 4 Soldiers, as a Platoon Leader I had 36, and now as a Company Commander I have 90. While on Staff I was supporting a Battalion of 500 Soldiers, and my failures/successes impacted each and every single one of them. As a Soldier myself I remember going into numerous Training Exercises underequipped, under resourced, and under managed. As an Officer I can generally safeguard my Soldiers from these same problems to the upmost of my abilities. I can impact Soldiers, NCOs, and Officers and make better leaders.

My only regrets with commissioning have been loss of camaraderie I felt as being part of a Small Unit. Furthermore, in many aspects I don't find my day-to-day duties as enjoyable as I did as a Soldier. I'm no longer the guy in the breacher stack or on the support-by-fire line. However, despite this I'm overall happy with my decision to commission.

Best of Luck. Keep your grades up, they'll the deciding factor when it comes to your Branch Preference List and if you get your #1 pick.