Unless you just can't spare the space of a desktop, I'd really recommend a desktop rather than a laptop.  Daily use on a consumer grade laptop just physically wears out the lid and stuff too much for a long use lifespan in my opinion.  I sure wouldn't get an Inspiron wanting to use it for 7 years.  A Latitude with a magnesium chassis maybe, but not a plastic Inspiron.

I've had the same Dell Optiplex desktop for 5 years that I bought as a grade B refurb from Dell Refurbished and it has been running 24/7 and used daily and still runs fantastic.