I have a Toshiba 52XF550 and I think SD is acceptable on it. The screen is not glossy but the bezel surrounding the screen is high gloss. Because the bezel is very thin (3/4") it really doesn't cause any annoying reflections.
SD quality varies due to many factors: the compression level used by your cable company (which sometimes varies from channel to channel), the cable box, and the scaling capabilities of the TV. Some TVs do a better job than others but I think the Toshiba does a pretty good job. SD on the premium channels often looks way better than SD on the regular channels, presumably due to lower compression.
If your seating distance is 2-3x the diagonal measurement of the TV, you won't see any better details from a 1080p TV so you could consider getting a TV with a slightly lower native resolution, like 720p, because a SD (480i) image will look a bit better than blowing it up to 1080p.