We present exact expressions for the average bit error rate (BER) and symbol error rate (SER) of different modulation techniques of a wireless system with multiple transmit and receive antennas. The receive antennas are assumed to use maximal ratio combining (MRC), whereas the transmit antenna that maximize the instantaneous post-processing signal-to-noise ratio (SNR) is selected. We consider an independent but non- identically distributed (i.n.d.) Nakagami-m fading channel where the long-term SNR and fading parameters from the different transmit antennas are arbitrary and may be different from each other. For the case when the Nakagami fading parameter m has an integer value in every channel, results are given in closed- form as a finite sum of simple terms For the case when fading parameters take any real value, our results are given in terms of the multivariate Lauricella hypergeometric function F A (n). Monte Carlo simulations are shown to validate our theoretical analysis.