Nothing beats having a look at the products yourself and seeing how they would fit in your environment, where possible but if you haven't seen it yet, the Magic Quadrant for PC Configuration Life Cycle Management Tools report may be of some interest. It doesn't cover the newer 7.1 releases, which looks significantly better than the original 7.0 release.

If you did want to look at an alternative solution, this would get you up and running pretty quickly.

I believe the big factor for us is that SCCM doesn't have as much non-Microsoft support at Symantec products.  Allthough I have heard that it will change in upcoming releases.  I can't speak to Landesk.

I would agree with most of the findings from the link

 SMS was extermely low in its CMDB functionality

the SCCM product is very immature in its CMDB implementation. However, they are coming on hard and fast to try and catch up.

the Altiris product is much better at its CMDB implementation howver 7.0 maturity is a little lacking. I am finding this out right now doing a 7.0 implementation. I will doing a 7.1 uprade soon in hopes of catching some upgrades. Symantec really needs to fix its stability issues in 7.x

LanDesk is very low in my last look

HP Asset Manager smokes everyone right now in the demos that I have seen. Plus they have 2 years jump on everyone else right now.