I have a four-year-old Toshiba WLT68 32in that's "HD Ready" rather than the full 1080p. With both my SA and Samsung V+ boxes I set them to 720p as I found that best handled fast motion and didn't feel like any kind of HD compromise on that size screen. With the V+ SD channels PQ varied very much depending on the quality of the source; the BBC ones were very good, Sky ones notably poor. The further down the EPG you ventured the weaker the SD results.and more recently
With my TiVo I found that it had defaulted to 1080i, and the SD channels were softer and the colours looked artificial - for example, I watched Spectacle on Sky Arts 1 in SD over the weekend and it was particularly soft, almost blurry. Eughh.
So I changed the setting to 720p and the SD improved; Rubicon recorded from BBC4 looked very good indeed, on a par if not slightly better than my Freeview BBC4. The few remaining SD menus on the TiVo looked better too. My recording of Spectacle still looked soft to me, but not quite as bad as when the TiVo was set to 1080i. I then did some switching between the SD and HD versions of ESPN and Film4: I'd say that they appeared very similar to what I had on the Samsung V+.
I think it's pretty subjective and very much depends on which SD channels you watch: the SD bitrates are probably as big an influence as the hardware if you ask me. Of course, having a 32in 720p TV is not going to have the same issues as a larger 1080p display, but then unless you've gone plasma I'd suggest SD is always going to be soft on anything above 40in, regardless of upscaling
If John's finding more recently filmed SD shows just as bad or has a preference for older material then he may be better off with the V+. The earlier episodes of Friends never looked good to me on the V+ and even the later ones aren't that great in the PQ stakes. I'm surprised they haven't upscaled them to nearer HD quality like they did for the Seinfeld DVDs a few years back - those look very good compared with the original broadcast versions.It's an interesting thread if you are considering TiVo but watch mainly SD channels, well worth a read before placing an order for TiVo.
The reason there's no consensus is people have different TVs, sizes and viewing habits. As I said in a previous post on this thread I watch very little SD now and only go there for stuff not available in HD - Rubicon on BBC4 (picture quality good); Justified on Five USA (PQ better than Freeview but not great); and BBC News (PQ variable). For me, a couple of hours a week of SD wouldn't be reason to abandon TiVo, especially as the 720p setting improves things a little. And, ideally, Rubicon would be shown on BBC HD and Justified on Five HD - both are quality imports and would be preferable to the constant repeats on the former and much of the SD tosh on the latter.