Hi!
The effectiveness of a teacher will have nothing to do with their status as an independent or an employee. A good teacher is a good teacher. That being said, some studios control their teachers more than others and certainly some studios put a premium on a person's ability to sell rather than to effectively teach. The only way to know who is right for you is to give them a try. When you sign up for a lesson, be sure to clearly outline your goals so that they know what to focus on. Since you are in the try-out stage, just take a lesson or two, and don't commit to anything further until you've tried out all the people you are interested in. Then, take a day or two to sleep on it, and then make your decision.
This will help you find the actual teacher that you like. However, you have to keep in mind that there are things that a studio can provide that an independent teacher cannot, and visa versa. An independent will probably be a lot more flexible than a studio employee, as they have to answer to no one other than themselves. They may or may not be able to offer package deals, accomodate to your schedule, and may even be willing to drive out to your area. That being said, a studio can provide a social setting that an independent cannot. A studio has parties and events and functions that will allow you to meet lots of other dancers and provide you with many opportunities to dance socially. Take Arthur Murray for instance. it is very true that the level of instruction is usually quite bad. Arthur Murray is not a place to go to become a champion dancer. That being said, if you want an amazing social scene, these people know how to entertain. You will pay through the nose for it, but you'll have some fun, but probably not advance much as a dancer. I liken it to joining a country club.
The reason I bring all of this up is that you must be clear on what you are looking for. If you really just want to improve your dancing abilities, try out a variety of teachers, and unless the studios create problems (such as squeezing you to take more lessons and such), there isn't any good reason to not try out studio teachers in addition to independent teachers. If you need a good social scene to go with your lessons, your task will be a bit more tricky as you will probably be better served with a studio teacher, as it will give you access to studio events (although many studios let non-students join their parties too!).
Forgive me for the long post. I do hope you find someone that will help get you where you want to be. Best of luck!