Monitor vs HDTV

I'd get the monitor. HDTV's tend to support less connectivity standards and (sometimes) have trouble handshaking with graphics hardware found in PC's. I'm going to guess that the monitor will have a better response time for gaming which you might not find, not to mention a better pixel density so your picture won't look as pixelly (assuming they're both 1080).

One annoyance with using an HDTV vs. a monitor is that the TV will not turn off when you turn off your computer. The monitor will go into Standby mode, but the TV will need to be physically turned off every time. I found this out when I connected my monitor using an HDMI cable, it caused the PC to treat it like an HDTV and the lack of Standby mode made me switch back to DVI.