The Zenith DTT901 is better overall, but the RCA may be easier for some people. Below are just a few of the more important differences.
Advanced features are accessible from buttons on the remote with the Zenith, but you must use the menu to access these features on the RCA. Someone who is not likely to use any of these features will like the RCA remote better because it has fewer buttons and larger buttons.
UPDATE: I like the EPG on the RCA better, but both only show now/next and you must access the menu to view the RCA EPG.
The RCA remote controls the volume on the TV. The Zenith remote controls the volume output from the converter box.
The RCA cuts off a little more of the picture than the Zenith. (More overscan?) UPDATE: This appears to be improved on the new RCA model.
The Zenith color is less vivid when connected via the RCA plug.
The RCA does not allow manual addition of new channels, the Zenith does. This is only an issue if the RCA unit won't pick up all stations because of station direction. UPDATE: The DTA800B1 now has the option to add to previous scans.
The RCA breaks up and takes more time than the Zenith to recover if you walk in front of the antenna and block the transmission. UPDATE: I have the DTA800B1 hooked up to an attic antenna so I cannot say if this has improved.
The Zenith has RF pass-through, but that difference will be gone when the DTA800B1 becomes available. UPDATE: As expected, this difference has disappeared, but the RCA needs to be on standby for a clear analog pass-through. If you unplug it the signal is not as good. I found no difference with the Zenith unplugged or on standby.
The Zenith has more picture modes. This again may not be as good for the less technically oriented.
UPDATE: The sound output on the RCA is slightly lower when hooked up to the RF cable then when hooked up to the line inputs. I did not notice this with the Zenith.
UPDATE: The RCA remote has significantly more TV codes than the Zenith. The Zenith only has 45.
In short, if you are getting the box for someone who is technologically challenged, the RCA may be better. The remote is simple and the viewing modes are limited to a choice between the two screen ratios. Overall the Zenith is better though.
UPDATE: My overall opinion of the two units has not changed. The Zenith seems better built and probably performs slightly better overall, but I still don't like the fact it's remote does not control the volume on the TV. It also includes A/V cables, the RCA still does not.
The RCA is a good unit. It's decreased number of viewing modes and friendlier remote makes it ideal for someone who only wants to turn on the television, change channels and adjust the volume on the TV. It does not have a previous channel button on the remote, but most individuals who want just the basic features stated in the last sentence don't use that feature. Of course, none of this matters if the remote cannot be programmed for your TV.