If by "simshaker" you mean a jetseat with 8 vibrators, yes, that´s better than a single unit buttkicker. The ability to notice side effects like huey door gunners, cannon position, from what wing drops a bomb and such is a great tool to have on DCS.
Also bear in mind both systems can be add up, taking full advantage of their strengths. Buttkicker is great for effects like touchdown, burner, engine...