In general, the most important things to be considered for a competitive residency (location or specialty) are grades/ranking/AOA status and board scores. Assuming you have that part complete, research experience will definitely help you stand out, and may be considered more important for some specialties than extracurriculars. Generally, basic science (lab) research seems to be considered "more impressive" if only because that is more relevant to fellowship (post-residency) training. However, clinical research does seem to be looked at favorably, and is probably better than doing no research.
In general though, most med students will tell you not to do research just to pad the resume -- only do it if you are really interested in it.
I'll move this over to Rotations and Residencies where you will probably get better advice.