In mode division multiplexing (MDM) transmission system using few-mode fiber (FMF), mode differential group delay (MDGD) is one of the key factors that influence the system performance. Considering the practical fiber fabrication technique, the MDGD characteristics between different modes of step-index (SI) fiber, graded-index (GI) fiber, trench-assisted SI fiber, and trench-assisted GI fiber are numerically investigated. Under the condition of supporting four modes, two optimized refractive index profiles of FMFs with high and low MDGDs are presented. The high MDGDs of LP11, LP12, LP02 versus LP01 are 4.65, 10.02, 11.73 ps/m, respectively; while low MDGDs of LP11, LP12, LP02 versus LP01 are -0.049, -0.258, -0.168 ps/m, respectively. We fabricate and characterize the FMF with a SI profile, whose loss of fundamental mode is 0.23 dB/km at 1550 nm and 0.37 dB/km at 1310 nm. The measurement and analysis results indicate that it can be used for future MDM transmission system.