Image format Export DPI  Quality Arcsize Irfanview size if quality = 100% Quality reduction needed to get Irfanview equal file size
Program % kb
JPEG ArcView 300 100 1257 1062 n/a   Too big, no improvement
JPEG ArcView 300 80 443 954 86%   Good quality
JPEG ArcView 300 60 338   77%   Lines begin to blur
EPS New ArcView 300 n/a 749 n/a   Better for vectors than the JEPG format, lot worse for raster at 300dpi than the JPEG is
    Conclusion: Best for keeping vectors editable (like symbols from Arcview into Illustrator)
EPS New ArcView 600 n/a 2143   Slow, big, about same quality for raster as a 300dpi jpeg, no improvement on Vector of course
Only if desperate to use one format for raster/vector combination file but still not great
Cannot preserve text of e.g., the legend in editable format
CGM Bin ArcView 300 n/a 310   Vectors good but raster crap, and cannot ungroup anything inIlustrator
CGM Bin ArcView 600   691   Slow, not big; vectors good raster same as 300 jpeg but still not ungroupable
    Cannot preserve text in editable format
CGM Bin is similar to EPS but worse because of no ungrouping
CGM Character ArcView 300   333   fast but no use for neither text nor anything else, you get nonsense
CGM Clear Text ArcView 300   fast but no use for neither text nor anything else, you get nonsense
EPS Old ArcView     Cannot yet find difference with EPS new, except New has more dpi options
WMF Placeable ArcView 144 clip no 230   Very similar to CGM and EPS, editable like EPS, and good for vectors but bad for raster, but 
  300 clip yes 721   ungrouping gives worse results than EPS, so EPS still better (WMF ungroups all vectors, but
EPS first ungroups them into similar groups, which could be handy, i.e., vectors with different ID's
and hence different legend symbols, stay grouped, which makes editing them easier
Conclusions:
1) Use JPEG at 300 dpi and 80 quality if using raster/vector combi  in your layout and if everything in your layout is already perfect, no editing needed; see attached script for this exact purpose
2) Use EPS to export vector files and legends which require manual editing (text + vector symbols) in Illustrator, and then manually add any raster files, then export as JPEG from Illustrator
Use attached script at 300 dpi, since higher resolution is a waste since they are vectors files anyway
3) If you have a licence, use Mapublisher to import most shapefiles into Illustrator, use EPS only when exporting geological symbols, and combine them in Illustrator
4) Alternatively, if you prefer Illustrator's geological USGS swatches (fills) above ArcView fills, but do not have Mapublisher, use the Select>Same>Fill color etc. options in Illustrator to quickly change
the fill or stroke of all polygons for example that have the same ID and thus same fill in ArcView. Then you have the same functionality as with Mapublisher, except for the reprojection options of raster files
More info on export formats in ArcView http://support.esri.com/index.cfm?fa=knowledgebase.techarticles.articleShow&d=18810
or:  http://members.westnet.com.au/bhulscher/exportlayoutscript.mht
Download scripts TSRC FTP