What dnmilikan said. Also, most paper developers tend to "warm up" the image as they age. So if you wanted to warm up a neutral or cold print you could use aged developer. But if you want to keep the image as neutral as possible you should use the freshest developer and a longish dev. time. A short Dev. time will also tend to produce a warmer image because the development has not gone to completion.
Probably most of the developers still available at the camera stores will produce a good neatral tone if used correctly. If you are mixing your own then what dnmilikan is very important, but the two that are probably best known as neutral-tone developers are Ansco 130 and Dektal