Here comes that [email protected]*N hillbilly with more opinions! It really depends on your situation. If you are hunting an area with a lot of buck sign, coming in to the rut, a grunt call will simulate a rival buck looking to take over some territory, and does. A good curiosity call, again during the rut, is an estrous doe call. This will simulate a doe ready for breeding, and works well in conjunction with a doe urine. Rattling is good for an area with a high buck concentration, bringing in other bucks to watch or try to run off the ones fighting. A tending grunt mimicks the sounds a buck makes while tending a doe, and is really effective if the rut is in full swing. Again, this will signal the dominant buck that an intruder is in his area, loving on "his" ladies.
I have sat back on southern AL greenfields and watched deer respond to the calling of others. Like ducks, the less a deer has heard, the better the chance to fool him. Most of the ones I observed, heard something wrong and quietly headed in the opposite direction. The hunter would have had a lot better chance at a deer by just staying quiet and not trying to influence the deer. The key is to use a call sparingly, and realize it's a handy tool, but it won't overcome any other shortcomings, such as scent control, making noise, and basically, being still and paying attention to your surroundings.
I've had better luck w/ rattlin than I have w/ calls. I have used a grunt to get a moving deer to stop long enough for me to get a shot. But I've never felt like I managed to "call" one in. On the other hand, using a pair of old sheds, I've have managed to get deer to come to me.