I would say no. But in 2-3 years time, things could change for NB. Lowell has better access and has been redeveloping longer than has NB.
This, but I think the differences between the two are great enough to make comparisons tough.
I think Lowell has positioned itself well for commuters to Boston who want an affordable urban living situation. I work near North Station and drool over the thought of 1,800 square feet in a converted mill, urban amenities within walking distance and a fairly painless commuter rail trip in every day.
As much as I love New Bedford, I don't see it ever being that type of commuter option (short of high speed express trains to South Station). I'd attribute most of its redevelopment to being a semi-independent (certainly more detached than Lowell) urban center with good bones. Downtown New Bedford fills an urban void for a region that has to travel to Providence, Boston, or Newport (to a lesser degree, you could include Plymouth) for the next urban center.
The city as a whole isn't really improving. The infrastructure is getting better. There are some great aesthetic projects (exposing the cobblestones, Route 18 redevelopment downtown, Acushnet Ave. in the North End, etc.) and downtown has certainly seen a resurgence of interest with lots of little stores and restaurants, but most of the city is as bad as it has been for a long time. Much of the traffic downtown is people from outside the city.
New Bedford should focus on making better use of its natural harbor and seaport (one of the things that separates it from Lowell), its airport, and encouraging BCC and UMass Dartmouth to expand their presence downtown (their current presence is definitely already a boost). I don't know that it'll ever be as built up as Lowell, nor will it ever be the commuter hub Lowell is. It needs to focus on being a semi-independent working seaport city not TOO far from Boston and Providence.