It depends what you need - insurance, tracking, COD, airmail, etc.
Check these sites for rates that are more specific, there are too many variables to say "shipper X is better."
If you're shipping out of the states:
http://www.usps.gov
http://www.fedex.com
http://www.ups.com
http://www.purolator.com/usa_customer/index.html
http://www.dhl-usa.com/index/
Or if you're shipping out of Canada:
http://www.canadapost.ca/segment-e.asp
http://www.fedex.com/ca_english/
http://www.ups.ca
http://www.purolator.ca
http://www.dhl.ca
Hopefully those are some good options to check out. They should all have some sort of rates on their sites - the only one that's a little iffy looking to me (might not be a very good site) is dhl.ca - but I haven't looked that deep into it.