The paper is focused on control of single-input single-output (SISO) systems with harmonically time-varying delay. Three different approaches to continuous-time control are presented and compared. The first technique uses a modified PI-PD Smith predictor in combination with standard forms for minimum of integral squared time error (ISTE). The second methodology is also based on modified Smith predictor and on design by coefficient diagram method (CDM). And finally, the third approach to synthesis is grounded in general solutions of Diophantine equations in the ring of proper and Hurwitz-stable rational functions (R PS ) for 1DOF control system. The comparison of methods is performed and illustrated on a simulation example.