Well the answer depends on the material that you're planning to watch most of the time. HDTV's produce a much smarper, clearer, vibrant and detailed image in comparison with regular TV's but only when watching HD material. SD (Standard Definition) material however looks blurry and soft on HDTV's due to the lower resolutions of the video and therefore looks better on regular TV's.
So bottom line is:
SD (Standard Definition) material (DVD, normal TV Broadcast) + SD Gaming (PS2, Wii) = Best viewed on regular TV's
HD (High Definition) material (Bluray, HD Broadcast, HD-DVD) + HD gaming (Xbox, PS3) = Best viewed on HDTV.