What branch should I choose upon getting commissioned?

Infantry: if you're not in it, you're supporting it!

I was both in it and supporting it. Never in the Guard, but there was no Aviation Branch in 1965 when I went through Rotary wing flight school. After a tour in Vietnam (118th AHC) I was getting short and was going to make it a career. I thought about extending for a ground tour to keep my Infantry creds., but then got orders to Fixed wing school. I asked a senior officer, whom I trusted, and thought was very old, (I was 23, he was maybe 34-36) for advice. He told me that there would soon be an Aviation Branch and, when I was his age, would I rather be humping a ruck or flying. I loved the Infantry, but in "old age" I thought I would rather fly. I told him I would rather be flying. He told me I had answered my own question. I went to FW school, then Rucker as an attack helicopter instructor and back to Vietnam in 1969 to command the OH-6A Training Team. I resigned my Commission in 1970. I went on to fly in civilian life for another 35 years in law enforcement, Alaska, and Fed EX. No regrets! What you learn in the Army will always be a plus. Aviation is a real big PLUS. Think long term. Good luck, and don't run out of pitch, power, pedal, and ideas at the same time. Bob Hoffman, Bandit 32 / Superbee 6.

Thank you sir

Side note, if you're planning to go active, there are criteria you have to meet based on what rank you are, i.e. LTs need KD time and must be fully qualified, same with CPTs. It's also based on needs of the Army, if they don't need aviators, you'll be out of luck.