Having experiences with both (CR and SSRS) here is the lowdown of what I think:
CR lets you develop a report very fast. As long as its simple. If it gets slightly complicated, it gets fishy trying to make it do what you want. Per example you are limited to a max hierarchy of 2 subreports. It gets weird when you have subreports that need parameters that must be altered in a main report, etc. Plenty of workarounds but sometime they simply suck.
Also the report layout is basically fixed; you have to put your data and info into the specific sections (Page Header/Footer,Details/Report Footer/Header). This is rather helpful as it helps you correctly display data that spans on multiple pages.
Also it has a fairly complete set of functions that can be used to manipulate financial data and etc.
SSRS is more flexible around the report editing. Its report wizard allows you to basically create a report in a WYSIWYG environnement, it allows you multiple subreports so you can easily display multiple datasets in one page. It allows you to connect .NET assemblies to do complicated data manipulation/calculation. However, it can get hard to properly display your reports in a fixed way, you often have to struggle to get everything displayed as you want it.
Crystal Reports is $$$.
SSRS, if I remember correctly is now bundled "free" in the SQL Server Enterprise edition. Of course you probably pay for it in the price of the whole package, I guess it's MS way to try and push it in corporate land.