Martigues

Hi.
"Conflicting reports" is a nice way to put it. In two years of leaving in Marseille I rarely heard anything good. I went to see for myself : it's actually not that bad, as the three old towns (Martigues is the reunion of three villages) are quite cute. But there are few interesting shops and restaurants, so I couldn't see myself lingering more than a few hours.
And the outskirts are terrible, with oil refineries on each side - it does smell when the wind blows the wrong way. There is also little of interest within 30 miles (sure, the coast south east of Martigues is pretty, but quickly visited). And while a scenic railroad links the town with Marseille, you would still need a car for any other meaningful sightseeing.

Long story short: don't settle there for a week. Neither should you consider nearby Istres.
If you are looking for an off-the-beaten-path Provence town, Salon, further north, is much better.

We stayed in Martigues for one night because we were flying out of Marseilles, and someone we met in the Languedoc had a relative there and said it was a nice place. It wasn't. Not that it was the ugliest place I've been to, but it didn't really have much to recommend itself to a tourist. Especially not for a week stay.