I've tried slicehost, linode, and mosso (now rackspace - cloud servers) they were all pretty similar. I think the new linode pricing now matches the old mosso pricing.
It matches the old Mosso prices minus bandwith. If you use a considerable amount of bandwidth Linode will be more cost effective.
Not only that, but Linode doesn't cap bandwidth based on node size. I've been able to get up to almost 200 Mb/s out of a Linode 360 whereas the smallest slice (256) is capped at 10 Mb/s