I trained with one on the Starting Strength lifts for 4 months. Made crazy gains, but I ended up stopping after an injury. I was not listening to my body the way I would have if I hadn't had the trainer.
I'm starting Crossfit now, and my number one goal is zero injuries. I like that it's more of a class format than it is a one on one training format. I can go at my own pace.
I used to think the same way. But gyms vary widely in quality and culture. And you can go at your own pace, nobody is going to make you do more when you're ready to stop.
I personally would prefer to just lift. But unless you're pretty lucky, or are willing to invest the time and expense, you won't have access to a gym with decent equipment. Since convenience is a huge factor in lifestyle choices like working out, you need to choose amongst the activities that are close to you. Once I graduated from cardio at Planet Fitness, the only place to go really is Crossfit.
