Are you playing back from a hard drive?
H.264 would probably be your best bet.
> mov will not work because it runs so slow and the filesize gets to big.
This statement raises a yellow flag. You need to know that the .mov (QuickTime movie) file type is jsut a container. It can contain video encoded and compressed in many, many ways. You are likely just seeing that the default encoding options for QuickTime movies from AFter Effects results in large files, because the default is lossless encoding with the Animation codec at the highest quality settings.
I'm not saying that a QuickTime movie is the right thing for your purpose; I'm just saying that you shouldn't discard it without understanding what it is.
I tried H264 but I get an error in AE when I start to render.
So, if I decide to use MPEG2 DVD (which works), how do I make the movie
"strech" all over my widescreen monitor? Im exporting as a 16:9-movie but still,
it doesent strech out.
Anything in standard definition (MPEG for DVD, for example) is going to look blurry on an HD television.
How are you playing your video back? If it's on a DVD, then just make sure your DVD burning software is set to 16:9 anamorphic. If you're playing it from a computer, you can output from AE as square pixels.
What do you mean Blu-Ray is too slow?
Also, I should mention this great advice from Dave LaRonde at CreativeCOW.net:
"Don't use AE to compress files for final delivery. The various compressors are there only to make quick 'n dirty files showing a project's progress to producers, clients, the kids, etc. AE is incapable of doing multipass encoding, a crucial feature that greatly improves the image quality of H.264 and MPEG-type files in particular.
Render a high-quality file from AE, and use a different application to do the compression. Popular ones are Adobe Media Encoder, Sorenson Squeeze and Apple's Compressor, which comes bundled with Final Cut Suite. Even compressing in Quicktime Pro is better than compressing in AE.
Making good-looking compressed files is almost as much an art as it is a science. It is NOT straightforward at all. I recommend asking a few questions at the COW's Compression Techniques forum."
Edited to add the advice about not using AE for final output