Everybody has their favorite call and their favorite kinds of calls, but you need to remember that it's all about what's relevant to you.
Myself, I prefer pot calls, and mouth calls, but carry a box call as well. I also know guys who can't use a mouth call, and other guys who use a box call because that's what they feel comfortable with. I've known guys who have had very expensive calls and still could not call very well, and other guys who had cheap calls, and were excellent callers.
So, I guess what I'm saying is to remember to take everybody's suggestions on this one with a grain of salt. The suggestions on here should give you a good place to start looking, but make sure you are comfortable with the call(s) you end up using. Because if you're not comfortable with your calls, you'll probably never be as good of a caller as you want to be.