I know, i know, perhaps this might have been asked before but the infos can be outdated.. we are 2011 for gods sake..

Just.. answer the question..

(it really depends on the type of file, just say what you use it for, what you compressed, what was the output.. etc.)

also is this some dream???
http://img204.imageshack.us/img204/2542/92688595.png

Extreme compression ratios are possible on certain file types. I don't think I've ever had 1%, but I've had in single digits on some MIDIs.

Honestly, with disk space and bandwidth always rising, what matters is compatibility. So just go with gzip or bzip2 if it's going to be mainly needed on Linux, or zip or maybe rar if it's being shared with Windows people.

The best is xz or lzma or 7zip (with lzma), at least for compressible, non-random files.

For multimedia, I'd say h264 for video and aac for audio (or vorbis). Sometimes xvid is equivalent to h264, but it's rare.

I've always found .rar to be effective. 7zip is nice, though the Windows program itself is a memory hog.

I think I'll agree with H_TeXMeX_H on this one; *.xz is really good...Arch uses it for its packages, and it really speeds things up download-wise (compression ratio is usually excellent).

7z or rar/winrar. maximum compression, solid archive. "rar a -s -m5 archive.rar files" or "7z a -ms=on -mx=9 archive.7z files". Results are more or less same (if you didn't delete rarfiles.lst by accident), except that 7z eats too much resources for that. There are tools that can compress better, but they aren't that stable and literally take forever.

1TB file that contains only zeros will compress into ~20 kilobytes on any decent archive. Also see "archive bomb".

That's lossy video encoding - different story.

Yes, but the OP mention any file type. For loss-less audio use flac. For video ... I don't know of any.

HuffYUV and Lagarith, which are open.

The Quicktime Animation codec, which is proprietary.

These are all designed for compressing video for editing, so they use intra-frame compression. The cost is that file sizes are large. SD-resolution HuffYUV video is around 5MB/s.

There are some video presets for libx264 in ffmpeg that go by "lossless_*". Not sure if this is losslessly compressed or straight uncompressed video, but I'm betting on the former.

EDIT: Ninja'd...dugan beat me to it.

i pretty much liked 7zip too.. actually is one of the first things i install on new os installations: p7zip on linux or the 7zip GUI for windows.
i agree, it uses lots of memory, but todays standard is at least 2GB ram or more. that is plenty to use with 7z even with windows.
i don't like rar because i have to pay for it..i always felt that rar was a monopoly (everyone split their files with rar for rapidshare, megaupload etc.)
for splitting files i want to get out of the monopoly...
whats your opinion about PAQ compression algorithm?
is bzip2 compression ratiio as close as to the one of 7z?
is zip any good?

If compression speed is not a big issue, xz is by far the best.

It takes very long to compress, but the ratio is better than any other formats I used and it extracts very fast.

Also, I think that the fact that Arch Linux and Slackware are switching to it for their package format sure says something.

Dirac and Theora supposedly are lossless.

it gave me kinda the same results as 7z..

anyways, seems that PAQ format is a winner in ratios...

Linux Format magazine did a review of archivers a few months' ago.

For a mixed directory, the best compression was 44% with lzip and 43% with lrzip and 7z, compared with 39% for gzip.But gzip was 22 times faster.

For a set of 100MB files, the best compression was 36% with lrzip, compared with 30% with gzip. Here, gzip was 4 times faster.

For a stack of jpegs, compression was between 2% and 3%: they're already compressed. But gzip was still twice as fast as the nearest competitor.

For decompression gzip won hands down: 53 seconds, compared with 127 for 7z, and 164 for lzip and lrzip.

The conclusion was, if you're desparate for space use lrzip; if you want to save time, use gzip.