Turkey is better for you, but don't believe anybody that says it tastes just like beef. It doesn't. Its not bad, but its also not beef. It needs to be seasoned very well, or its not very good at all.
If you learn how to make good ground turkey then its a great substitution. It took me a good 3 tries before I started substituting it in on a regular basis, but its still not my first choice of meats.