You have asked a difficult question as the lines between the two have becoming blurred.
The first question you need to ask yourself is what you are going to be using it for the most. A high end monitor will, as you say still give a better resolution than a TV. So if you are going to be using it most for gaming, I would recommend going for the monitor.
Between the two I would probably opt for the 26" HDTV.
To the best of my knowledge nearly all LCD HDTVs use 8-bit PVA panels which provides true 16.7m colors. I don't know of any HDTVs using the cheaper 6-bit TN panels, but I haven't researched any budget HDTVs.
HDTVs tend to cost less than the typical LCD monitor when both size and resolution are nearly the same. Perhaps the PVA panel HDTVs do not have to meet the same "stringent" quality requirements as a LCD panel for PC monitors. I don't really know.
The Dell 248WFP uses an "inferior" 6-bit TN panels. They are cheap to manufacture, and have fast response times for gaming, but they tend to have bad colors and produce image artifacts especially when displaying HD video content (I checked this out about 1 year ago). They also have poor viewing angles which means the colors tends to shift the more you lean left or right. 6-bit TN panels can only produce 256k colors, through a process called dithering, the remaining 16.5m colors can be estimated.
The 26" HDTV should be using an 8-bit PVA panel so you'll get the full 16.7 million colors, better blacks and better viewing angles so colors will not shift as much as a TN panel more you lean left/right. The chances of seeing image artifacts should be much less. However, these types of panels have slightly slower response times than TN panels; about 1ms to 3ms slower. But that's comparing a TN LCD monitor to a PVA LCD monitor. HDTV may have even slower response times.