That's a value judgement, and difficult to apply to an operating system. There's nothing wrong with Service Pack 1 after all!
SP2 contains all the updates that have been issued since the inital release of SP1, plus improvements to Internet Explorer, Internet Connection Firewall, improved networking features and security, and a host of other improvements, mostly security-related.
Like CatWeazle said, you don't compare the two. Service pack two has fixes that improve on the fixes contained in service pack one. Hence the term "Service Pack" sp1 is the first service pack, and sp2 will be the second.