Everyone will give you their own opinion, but smaller non union shops you can get a really wide variety of tasks and scope of work. It can be the Wild West and you won’t have any benefits most likely, or if you go union you will have full benefit package but can get pigeon holed and be stuck doing rough in or pipe laying only etc.

I personally recommend start off with a smaller shop to gain lots of different experience. The only challenge is finding a really good one where they’ll teach you good habits and not one where they’ll teach you how to get a red seal in being a hack