I agree, join the pipefitters if you like welding in circles and ending up where you began. ;)
As an Ironworker, I never once carried a piece of rebar except for the foundation of my garage.
Welding is the one career you can select that allows you to go as far as you want. I worked iron for many years before I earned my degree and branched out when the construction industry collapsed for a couple of years. My degree and CWI credentials gave me options that would not have been available otherwise.
It was never my intention to leave the trades. The trades offered the challenges and I met them head on. I worked the entire Eastern Seaboard over the years and had some exciting times. I burned rods, ran welding crews and erection crews. Each job was different from the last and each had challenges that kept the work interesting. I had opportunities to work overseas, but it was my decision to stay home with the wife and kids. There's no amount of money that would keep me away from them for months at a time.
I believe you need to figure out what type of work you enjoy and that is the trade to get involved with. Welding is a "tool of the trades", as such you can weld for any trade you select. If you enjoy grease and machinery, go with the Operating Engineers. If you enjoy welding in circles, go with the Pipefitters. If you enjoy being on top of the world as I did, join the Ironworkers. Any of the trades offers great opportunities for someone that is willing to do the work and doesn't mind getting a little dirt under the fingernails. I've taught welding for carpenters, electricians, masons, and others, every trade needs skilled welders.
As for the construction industry, union versus open shop is a personal choice. I've worked both. I prefer the training and opportunities offered by the union employers. From my experience with open shop, only the bosses make decent wages and usually they are family owned with family members making up the management side. The family get the cream and gravy, the workers get the scraps left over. I never had decent medical or retirement plan with an open shop employer. Overall, the union companies offer more to their workers than the open shop companies. So as a working man, I would opt for the union shop. Are there problems in a union environment, sure there are, but usually there is some recourse to solve the problem. You have to look at the aggregate, which environment will offer you more over your working lifetime.
Every shop wants you when you're young and strong, but will the same companies want you when you are older and don't move as quickly? I don't see many older men or women working for open shop construction companies. I wonder why that might be. Could it be a "hurray for me and screw you attitude" I see on many open shop job sites? Why are so many workers classified as "contractors" on the open shop job sites? Is it so the contractor doesn't have to pay workers compensation or benefits to the men making up the "gangs"?
As for working in the shop or in the field, I never cared for shop work. I enjoyed the variety offered by moving from one construction site to another. The core crew members were often the same people, but there were always new people in the crews and there were always new stories and lies to swap at lunch time.
My last word of advice is to look at the big picture. Where do you want to be in 10, 20, or 30 years from now? The choices you make now will determine where you will be in the future. If you don't want to work with your hands after a certain age, go to school at night instead of watching television. What ever your decision, pick a field you enjoy. I can't imagine working my entire adult life doing something that I didn't completely enjoy and offer me challenges that tested my intellect. That, working a job that I didn't enjoy, would be a waste of my life. That philosophy goes back to my high school days. The caption in my high school year book goes something like this, "If a man doesn't enjoy his job, he should find one that he does enjoy." I bought my first welding machine when I was thirteen and it has held my interest for the last 45 years. God willing, it will keep me happy and busy for the next 45 years.
Best regards - Al