The performance of the maximum-SNR design for multiple-input multiple-output (MIMO) systems is analyzed. An average symbol error probability (SEP), expressed in closed form, is derived assuming both i.i.d. Rayleigh fading MIMO channel and coherently detected M-ary PSK/QAM. This form highlights a modulation gain, which permits comparison of SEP performances between different modulations schemes. The maximum diversity advantage can be retrieved by using a Taylor series expansion around infinity from the exact SEP. The performance of the max-SNR MIMO systems is compared by changing the transmit and receive diversity, modulations and constellation size.