I have the option of doing research with my advisor this summer (yay, funding!) or working with a collaborator at a highly-regarded national lab (a research position, but called an internship). I have worked at this lab two summers ago, and it was very enjoyable, fairly productive, and I networked with people with whom I would love to work with in the future. I realized that this kind of work in this environment would be my dream job. To work there, however, I almost need a PhD (it's possible with a MS, but a PhD is obviously more competitive). Working at the lab has built friendships and has provided several networking opportunities since.
Unfortunately, the summer research at the lab doesn't further my dissertation. Working with my advisor does.
Should I go for the position at the lab for the summer, or should I stay and do research? If I wanted to work with the internship, how would I breach the topic with my advisor?