Raw audio usually means pure audio data (uncompressed pcm), and the file contains no information about the sample rate, sample length (8/16 bit), byte endianness etc. Therefore, a player cannot play the raw audio correctly unless these parameters are defined. Wav file on the other hand contains all the relevant information in its header part.
The codec used (uncompressed, ADPCM, ALaw, Mulaw etc.) when recording in wav format can make a difference in file size, but it shouldn't have any big effect on playback smoothness. For example, a good choice is to use a 8kHz mono wav, encoded with ADPCM codec.