As an undergraduate, should I graduate 1.5 to 2 years early with little research experience or 1 year early with a decent amount of research?
For the title question, graduating 1 year early and accomplishing more is definitely better than graduating 1.5 or 2 years early, and accomplishing less. In fact, there's a strong case to be made for taking four years and accomplishing as much as you can. In PhD admissions, you'll be competing against people who were also ahead of the game in their first few semesters, but stayed in school and kept gathering feathers in their cap. Some of these feathers will be more impressive than graduating early. Also, more time as an undergrad means more chances for professors to get to know you, and this is what translates into good letters of recommendation.

Now, that is all general advice. Factors particular to your situation may tilt the balance in favor of it making sense to graduate early. I would recommend talking this over with your professors, because they know your record and can give you realistic advice about your prospects after graduating in X semesters, for various values of X.