In this paper, we propose an optimal metric for detection ordering in terms of symbol error rate (SER) in vertical Bell-lab Layered Space-Time (V-BLAST) systems. Motivated by the log-likelihood ratio based ordering scheme introduced in , a new ordering method is presented which can further enhance the V-BLAST performance. The proposed ordering based on the new metric minimizes the SER by exploiting the instantaneous noise and considering its correlation at the linear filter output. A simpler suboptimal ordering metric is also proposed which requires much less computational complexity than that of the optimal ordering metric. We further show that there exists a simplified version of the suboptimal ordering metric for BPSK and 4QAM which achieves a significant performance gain over the conventional ordering scheme with no additional complexity. Simulation results show that the optimal ordering scheme achieves a performance gain of 13dB at a SER of 10-4 over conventional signal-to-noise ratio (SNR) ordering schemes with four transmit and four receive antennas. The performance of the suboptimal ordering scheme is shown to be less than 2dB away from that of the optimal ordering.