I've always rendered animation at 720x480 frame size, usually called SD.  As I've mentioned, I'm always in "48 Hour Film Contest" mode, (a 5 minute animation in 2 days), where "time is of the essence".  And however they project the videos at the theater showings, the 720x480 looks pretty good.  The producer just adds black bars to fill up the frame, I think - she knows what I'm doing ahead of time.  I'm reading that "HD" is either 1280x720 or 1920x1080, so I'm curious what frame size you Carrara animators are using.  My video editor can handle all this, but I'm still leery of render times.

It depends on what I'm doing.

If I plan on this thing being seen on larger screens, I usually do 1920x1080.

I don't know what kind of video you're doing (lighting etc), but if I were under your time constraint, I would probably 720x480 or 1280x720.

Depending on what kind of materials, lights are in the seen, you could have decent render times

Best of luck!

For online delivery, I use the HD 1280x720 format, simply to save render time. In fact, there are times that render a scaled down version and then up-rez it in the video editor to soften the look a bit and decrease the Carrara (or any other software) rendering time. But only if there isn't crisp detail needed such as text.

Yes, more pixels means better resolution but time is the trade off.

My broadcast stuff is sent to a render farm since they're now consistently requesting 2K and 4K output. Not enough hours in the day for that rendering in my studio. 

My first animation film, I did it in DV 16/9 interlaced (720x576) and the projections in the theatres were excellent.
For my new WIP, I make the renders in 1050x 576 square pixels progressive.
I made tests in a theater: the image has a higher quality than the HDV (live films).
I also made an upscaling in 720p and the quality seems better, but I believe that it's the projector which should not convert this format while the 576p is not a standard format.
I must add that I 'm working in postwork with uncompressed AVI and my renders are done in .tga or .bmp sequences.

OK, thanks all for the comments.  I think for now, at least, I'll stick with 720x480 since, as I mentioned, it looks OK on the theater screen at the 48 Hour Film contest showings (with the contest producer's help).  There are enough things that can go wrong in a 2 day, 5 minute animation, I'd rather not add another potential problem.  Maybe next year, after some experimentation ...

Mark B: "there are times that render a scaled down version and then up-rez it in the video editor to soften the look a bit and decrease the Carrara (or any other software) rendering time."

I assume you stick with the same proportions that you will end up with?

@ Steve K., Yes, same  proportions. The up-rez thing is actually a tried-and-true industry trick to add 'cinematic' quality to CG renders. And, by cinematic quality, I mean blurriness. Throw in a little film grain and presto, reality.

Mark, Okay thanks, I was not aware of that being a standard trick.  I'm curious how far one can push this - can you double the linear frame dimensions (i.e. 4x the frame area)?  Also, I wonder if that's more or less what happens when my 720x480 animations are shown on the same large movie screens as the live action HD entries ... altho I confess I don't know how they are projected, I'm just glad they look reasonable.

There is no good answer to that. Many animations are built with G-Buffers so they can be layered in the video editing program. If there is a depth of field thing happening, they asset can be even lower in resolution because it is intentionally blurred in the editor. 

But, as a rule, rendering at half size, and then sizing up will work ok. Push it beyond that and you will notice artifacts in near still scenes. But, if there is motion involved, viewers won't notice it. Motion trumps detail - every time. In fact, super detail is only for stills, never motion.

 Motion trumps detail - every time. In fact, super detail is only for stills, never motion.

Good point.  I do avoid "Best Antialias" for animated shots, and typically use "Fast AA" @ the standard 2 pixels.  But for those stills ... e.g. with a sailing ship's rigging, I use Best AA AND 0.5 pixel to get the rigging lines to not have gaps.  Throw in some Global Illumination and the 720x480 render time can blow the whole two day contest.  Happily, still images created before the contest starts are allowed, a big loophole ... uh, advantage for animations.