Go with the monitor. There's really no comparing 1080p to 720i, even if the one is bigger.
Do be aware though, that the Dell monitor will likely have rather limited input options. Likely D-Sub/VGA, DVI, and HDMI. So, you'll need to figure out an alternate solution for the Wii, which only does composite and component video AFAIK. You also need some kind of audio solution for the Dell monitor. Despite these drawbacks however, that will be by far the better solution long term.
I am looking to buy either an LCD TV or monitor.
I am not sure which would be the best choice.
I am either getting the Dell 24" S2409W(1080P) or Westinghouse 32" sk32H640G(720i).
I can get either for $200. Both are new, my friend bought the Westinghouse on Black Friday and never opened it and Dell has the monitor on sale for $199 which Best Buy said they would price match.
I have Xbox 360, Wii and HD cable.
Any help and suggestions would be greatly appreciated!