I don't have a lot of research experience but I have a lot of teaching experience
From an admissions standpoint, there are diminishing returns with any activity. If your research experience is objectively weak and you plan on applying to schools with a strong focus on research, it may make sense to have more research experience, especially if the research assistant job is different from prior experiences. Personally, I hated bench research, but found clinical research to be fun. So it's helpful to explore different types of research.
Having said that, a year of full-time teaching vs research will be looked upon highly either way. Consider the flexibility in schedules between the two gigs too to allow room for interviews and stuff.