What are you using it for? The second one's i5 processor is the 2nd generation series. Although it isn't quite as fast as the cpu in the first laptop it will achieve significantly better battery life. Besides that the Ram looks the same so I say go with the Dell if it doesn't cost much more. However, I'm no expert on laptops, so hopefully someone else with more knowledge can chime in here.
Id be using it for a home office. To write documents, log into citrix, but also to view video.
How can you tell that it is 2nd generation?