If your looking for an all in one type call the True talker is poobably one of the easiest.

If your looking for a grunt tube only then a number will work and are pretty easy to make a normal grunt sound. Of course if you want a doe bleat "the can" is pretty easy.

Personally I use only a buck grunt call, the rest of the sounds I duplicate by mouth.

A tape or video is a good idea as well, as it will allow you to hear different sounds and there meaning.