Getting into Grad school

does MIT require research experience to get into the Engineering-Aerospace/Aeronautical Program? Or is a summer internship with a large aeronautical co.(defense contractor) good enough?

No plans for a Phd.

stats: state school, mechanical engineering undergrad, 3.8-3.9 gpa, school requires undergrads to do a thesis for senior year

deciding if its better to work a few years or go right to grad school.

The graduate application process for Aero/Astro is described here (http://aeroastro.mit.edu/admissions/graduate-admissions). As a general rule, while research experience is not absolutely required, graduate degrees are research degrees, and the department will want to admit those who will prosper in this environment. You have three letters of recommendation. They should be from people who can talk to why you would prosper in that environment. A “he did well in my class” letter is much less useful.