I've used all 3...   I like them all.  I favor the 5700
by quite a margin but that's just a personal problem.  O :-)

None of these are SLRs by the way!

Read up on them yourself:

http://www.steves-digicams.com/2003_reviews/g5.html
http://www.steves-digicams.com/2003_reviews/nikon5400.html
http://www.steves-digicams.com/2002_reviews/nikon5700.html

http://www.dpreview.com/reviews/canong5/
http://www.dpreview.com/reviews/nikoncp5400/
http://www.dpreview.com/reviews/nikoncp5700/

etc.