OFDM suffer from a high peak-to-average ratio (PAR), caused by the addition of a large number of independently modulated sub-carriers in parallel at the transmitter. When subjected to a non-linear power amplifier, these signals may undergo significant spectral distortion, leading to both in-band and out-of-band interference, and an associated degradation in system performance. In this paper we compare between different modulations techniques in OFDM for the spectral efficiency, BER, and PAR reduction, which reduce the effect of nonlinear amplifier. Simulations of the proposed system models using Matlab are used to compare between three linear modulation families, namely M-QAM, M-PSK and MSK to be used for OFDM. Also we discuss the benefits of using MSK as the lowest crest factor modulation technique to be used for OFDM.