Tongue

1. They're more expensive. Its because extra work goes into fixing them. More trained professionals are needed.

2. Not everyone is a candidate for them. For some people, it may hinder while biting due to higher front teeth overlap.

3. Many people experience difficulty in speech. You may discover a lisp. It takes time getting used to. Although most people have been able to speak normally after a month or two.

4. Its more difficult to clean and maintain because they're on the inside but if you keep a very clean mouth then this won't be a problem.

5. Tongue soreness is often reported due to the scraping of tongue against the braces.

Take these into consideration and choose what's best for you. 

Hope this helps. :)