id go with the thinkpad because of the better processor over the dell and more ram. Honestly I don't think either laptop is a good deal. If you dont mind used/refurbished computers Id go to ebay and bid on a thinkpad t420 (14in ) or the smaller x220 (12.5in). If your lucky you could get one for under $400.
Thinkpads overall are a good choice due to their ruggedness and durability.