both jobs are good if you are looking at them to add somthing to your resume. but some schools really like the research experience over the other.pay varies from one school to other for research and at some places to begin with, there might be no pay, only a voluntary job.look at the diff school websites/research institutes for their research projects available needing an assistant.
the dental assistant job shal pay you more mostly, again depending on your certifications and the area you are working in.
i shal recommend a good work experience with both . good luck
