Solid-state implementations of quantum computing(QC) are particularly attractive because of the possibility of using existing computer technology to scale small numbers of qubits up to the 105 or so that would be needed for nontrivial computations. In this communication we examine the decoherence times for some of the existing proposals based on electron-spin qubits in the different Si-based heterostructures. We calculate the relaxation rate (1/T1) as a function of uniaxial strain, temperature, magnetic field and alloy content. In general, we find that the relaxation rate is strongly decreased by uniaxial compressive strain, making this strain an important positive design feature. Si-rich structures are to be preferred because relaxation time increases with increasing Si content in the investigated alloys.