If the laptops you're looking into have 1024x768 screens (unlikely, but possible), any of the cards you mentioned will do fine with Diablo III, and just about every game from 2011 or before. There are a few 2011 exceptions (Skyrim, Witcher 2, etc), and most 2012 games will probably not play.

If the laptops you're looking into have 1366x768 screens, or thereabouts (this is the most likely screen size), Intel HD 3000 is definitely out. Intel HD 4000 and Radeon 6490m both have roughly the same performance, and would do well if you turned the resolution down to 1024x768. However, games work better at your monitor's native resolution, and so I wouldn't suggest doing that. At 1366+ resolutions, these cards will struggle. With every setting at minimum, you MIGHT get framerates in the 30s, from what I've seen, but it's unlikely that the experience would be very good, and you'd see dips below 30 on a frequent basis. For games that don't degrade as gracefully as Blizzard's titles (read: virtually every other modern title), these cards are definitely not feasible at 1366+ res.

So. Yeah. In this case, it's pretty much a dead heat between the integrated and the dedicated graphics processor. The 6490m is, from what I've seen, in the same performance ballpark as the HD 4000. If you're sure that you can only pick between the two laptops you mentioned, I definitely wouldn't give up other specs (and pay more) to get the one with the 6490. You just won't see much benefit.

Ideally, though, you really need to spend a little bit more, even to play D3, but especially to future proof yourself just a little bit. I know that's pricey, but laptops do not make good gaming machines. You can buy a Desktop that will give you 100fps on high settings at 1920 for $500 - $700, but a laptop. . .not so much.