I had a phenomenal experience in the NG before I transferred to active. I’m a CBRN officer, and because I was one of only 3 CM LTs in my state at the time (NY), I got to go wherever I wanted. Additionally I spent almost all of my time in a full-time capacity through ADOS and SAD assignments (just keep asking for it, you’ll get it). Also got to deploy to Ukraine for 10 months, which was the best experience I had in the army. I’m on my 3rd active duty assignment now, and I’ve still never felt like I was part of a family, like I always did in the NG. I will say however, that the NG is a great place to go far if you’re competent. Very easy to make and keep great connections; but very hard to recover if you’re ate up. The reason for this is because people rarely leave the state. So the officers and soldiers you see in your first assignment will be with you 20 years later. You will always deploy with the same field grades. So when you make mistakes, they will be remembered.

Overall, I think the guard gets a bad rep because people really don’t understand it, but Being a full-timer in the guard was the best thing ever, personally. Whenever I tell my AD friends about my time in the NG, they’re always shocked that I left.

My experience in the Guard was not a good one as it was a “Good Ole Boys” Club. I didn’t wasn’t part of it so I was unable to get the training I needed. Once I transferred to the Reserves my career took off. But that’s my experience.

I served in the Guard as both an Infantry Officer and an Engineer Officer. For the most part, my experiences were positive, although I have had three commanders relieved for cause. I had the opportunity to attend a lot of schools, between schools and additional duties I probably averaged 100 duty days a year. When I was in, there were plenty of PL and CO positions in both Infantry and Engineer units (different states), and promotion through Major didn't seem to be an issue, although I left the Guard/Active Reserve before I was eligible.
If I were looking at choosing a Branch in the Guard, I would look at the units in the states I was interested in living. When I moved back to Ohio, they had a Separate Air Assault Infantry Brigade, and that was a good fit. When my civilian job moved me to Kentucky, they were short of Engineer Officers and solicited me to change Branches. It was the right move since Kentucky had two full Battalions of Engineers, one Corp level and one Divisional Combat Engineer (Mech). I served as Platoon Leader/Task Force Engineer, Company Commander, Assistant Brigade Engineer and S1 as an Engineer. Company Commander and ABE were the two best jobs I had in the Army.
Downside. Promotion above Major can be very slow, just a lack of slots and those in state are the only available. It is worse in Branches with a small footprint, which is why I would stay in the Combat Arms or Engineers. There are some schools that are difficult/impossible to get in the Guard. Airborne is probably the hardest if you aren't in one of the few Airborne Guard units, Ranger School is more of a possibility for Combat Arms Officers, but not an easy one to get either.
You hear nightmare stories about difficulty of transfer between states, but I never found that to be true as long as you know the rules AND they actually have available slots.