I compared the Roku LT with the Roku 3, flipping between two similarly calibrated inputs on the Sharp PRO-60X5FD. I primarily used the excellent-looking "Sherlock" as my reference material, and the difference was subtle at best. If I had to describe the differences, I'd say the Roku 3's image was ever-so-slightly sharper and the colors just a tad richer, but my overwhelming opinion was the two images looked nearly identical. The bottom line is the Roku LT's image quality looks excellent, and I'd say the vast majority of buyers wouldn't be able to tell there's anything "downgraded" about the experience.
However, if you're a videophile who won't be able to shake the notion that you're not getting the full 1080p experience, there's little reason not to spend an extra $10 for the 1080p-friendly Roku 1 to put those worries out of mind.
Chromecast vs. Roku LT
Google's Chromecast made a splash when it was introduced for $35, but most buyers will be better off spending the extra $15 for the Roku LT.
There are undoubtedly some areas where the Chromecast wins. It's even smaller than the Roku LT and its "stick" form factor means you can completely hide it behind your TV. The YouTube experience on the Chromecast is also flat-out fun, especially if you have multiple people contributing to a "party" playlist. (That's a particularly sore spot for Roku, which still lacks a YouTube app, although there are some decent workarounds.) And if you buy and rent content in Google's media ecosystem, the Chromecast is the best device to watch that content on your TV. (There's also screen-mirroring on the Chromecast, but in my experience it doesn't work all that well.)
But on nearly every other count, the Roku LT wins. It offers 1,000 channels, and while many of those are filler, there are a lot of great services the Chromecast is missing: Amazon Instant, HBO Go, MLB.TV, Spotify, PBS, to name a few. Roku's killer cross-platform search feature is another plus, making it easy to see where a particular movie or TV show is available.
The Roku LT's true onscreen interface also means you don't need a smartphone or tablet to browse content, which I find is better when you're kicking back to watch TV. In general, real buttons tend to beat virtual ones when it comes to the TV experience, especially if everyone in your household doesn't have a smartphone or tablet.
All that adds up to make the Roku LT well worth the extra $15, unless you're heavily invested in the Google media ecosystem.
Roku boxes compared
For a deep dive on the full Roku experience, check out CNET's full review of the Roku 3. Below is a breakdown of Roku's full product line.
Roku LT ($50): 720p video, HDMI and analog video outputs, available only at online retailers
Roku 1 ($60): adds 1080p video
Roku 2 ($80): adds Wi-Fi Direct remote with headphone jack, dual-band Wi-Fi
Roku 3 ($100): adds dual-core processor, motion control remote, Ethernet jack, USB port, SD card slot; no analog video jacks