This paper deals with the following issue in space time block coding (STBC) design: over a time selective channel,which scheme performs better, orthogonal STBC (O-STBC) or non-orthogonal STBC (NO-STBC)? It is shown that under time-selectiveness, once the vehicle speed has risen above certain value, NO-STBC always outperforms O-STBC - across the whole SNR range. Also, considering that all the existing NO-STBC schemes have been investigated under quasi-static channels only, a new simple receiver was derived for the NO-STBC system under time-selective channels.