Hate To Dig up an Old Topic. But I know People will hate it more If I start a new topic for the same reason. I did a comparison Test of sort on my PC. Intel Celeron 1 GHz, 256 MB SD RAM, WinXP SP2.
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7z V/S Rar V/S Zip V/S UHA
Used the following :
1 .7-Zip 4.15 beta	[Ultra Compression - Solid Archive]
2 .WinRAR 3.5 beta 6[Best Compression -Solid Archive]
3 .WinZip 9.0	  [Maximum Compression (enhance deflate) ]
4a.WinUHA 2.0 RC1 [ALZ(3) Best][Priority Normal]
4b.WinUHA 2.0 RC1 [PPM (Best-text Optimized)][Priority Normal]
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Format : Compression Format -> [Compressed Size]  [Time Taken]
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7.48 MB of Html,Htm,Mht,Txt,Zip [77 files].
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1 . 7z  -> 2.73 MB     41 sec 
2 . rar -> 2.78 MB     15 sec 
3 . zip -> 3.10 MB      11 sec 
4a. uha -> 2.73 MB    41 sec
4b. uha -> 2.73 MB    40 sec
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12.2 MB of SWf files [12 files]
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1 . 7z  -> 10.0 MB     35 sec
2 . rar -> 10.1 MB     26 sec
3 . zip -> 11.7 MB     13 sec
4a. uha -> 10.4 MB   98 sec
4b. uha -> 10.5 MB   163 sec
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10   MB of PDF Files [14 Fles]
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1 . 7z  -> 6.47 MB     52 sec
2 . rar -> 5.39 MB     16 sec
3 . zip -> 6.72 MB      9 sec
4a. uha -> 6.49 MB    75 sec
4b. uha -> 6.44 MB    107 sec
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10 MB Html file (PHP Manual)
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1 . 7z  -> 1.16 MB     68 sec
2 . rar -> 991  KB     11 sec
3 . zip -> 1.55 MB      6 sec
4a. uha -> 1.23 MB    55 sec
4b. uha -> 935  KB    20 sec
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10 MB PDF files (14 files), 5 MB HTML files (226 files), 6 MB DOC Files (101 Files), 6 MB of JPG files (100 Files) =27 MB
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1 . 7z  -> 13.5 MB     673 sec
2 . rar -> 13.3 MB      62 sec
3 . zip -> 15.7 MB      16 sec
4a. uha -> 13.4 MB    193 sec
4b. uha -> 13.0 MB     264 sec
================================
21 MB of Image Files (JPG,TIFF,BMP,GIF)
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1 . 7z  -> 15...MB      771 sec and Counting... *img138.imageshack.us/img138/1540/7ztime4rj.gif
2 . rar -> 17.6 MB        53 sec
3 . zip -> 17.8 MB        16 sec
4a. uha -> 17.42MB       165 sec
4b. uha -> 17.4 MB       290 sec
================================
Conclusion :
7z : New Format, Better than zip only in compression time, compression ratio better than RAR on only couple of occasions, VERY VERY SLOW, Only suitable 4 Small files <10MB.
zip: Most Commonly used , widely supported [compatibily], Fastest Compression and acceptable compression
rar: Not Free, Excellent Compression, Little slower than Zip, but way faster than 7z and uha. RAR looses out to uha in compression ratio in ->Image Compression, TXT compressions (eg:mht,htm,html,doc,txt..). But Loads better in Compression time.
uha:Free, NEW format, seems betterthan RAR in common formats [IMAGE,TXT..].Looses out in PDF,SWF formats.But takes longer time in compression of large files >10 MB.
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If time is a factor then RAR gives the best compression /time factor.
If Compression is what u want in Common files like IMAGE/TXT/.. use uha [ With PPM (Best text Optimized)enabled] 
