You should find this thread helpful. The initial comparison is made between the ASUS VS24AH (uses the same panel as the BL2411PT) and P2414H. Further down that thread the VS24AH is then compared to the BL2411PT, which will complete the picture for you.
The BenQ has a slightly more generous colour gamut (complete sRGB coverage), very slightly lighter matte screen surface and doesn't dim quite as far as the Dell. Really the main difference for most people is the 1920 x 1200 resolution (16:10 aspect ratio) and 24.1" screen of the BenQ vs. 1920 x 1080 resolution (16:9 aspect ratio) and 23.8" screen of the Dell.
The BenQ has a slightly more generous colour gamut (complete sRGB coverage), very slightly lighter matte screen surface and doesn't dim quite as far as the Dell. Really the main difference for most people is the 1920 x 1200 resolution (16:10 aspect ratio) and 24.1" screen of the BenQ vs. 1920 x 1080 resolution (16:9 aspect ratio) and 23.8" screen of the Dell.