I just completed a 200-hour vinyasa yoga teacher training in Connecticut. I hadn’t done much research beforehand so was quite lucky that I ended up in a good program. I knew I wanted a program that was Yoga Alliance certified, so looked up the registered schools on their website that were in a drivable distance from my house. The factors I considered were the style of yoga, the location of the studio, and how long the training would take (I wanted a course I could complete over the summer). Since there was only one summer training course within an hour’s drive of my house, the decision was easy.
If you live in a city, you will surely have many more options than I did and might consider the rigor of the program, how many students will be in it (in my opinion, the fewer the better so you can get more individualized attention), the background of the instructors, etc. I also recommend taking a yoga class at the studio, ideally with the instructors, before signing up for training if you can.
Also, if you definitely want to become a teacher, make sure your program is rigorous enough. I’ve heard of programs that had upwards of 50 students and to get certified, all you had to do was teach a few poses. After that, I would not feel confident enough to teach a class. On the other hand, that might be just fine for someone who wants to take the training for the sake of learning.
I hope that helped!