Agent catalogs inventory. The vendor doesn't make any difference except for availability of patches/drivers/etc., and the information that the agent gets from WMIC.
This has been my experience, anyway.
We have agents for all 3 - MAC if you chose to go that way, as well as Linux / Windows. The covered OS'es can be found in detail here: -- Supported Platforms and Compatibility Matrix for LANDESK Management Suite/Ivanti Endpoint Manager .
As long as you're using OS'es that we have an agent for, we're not going to tell you what you can use / whom you should buy from . Different features may exist for certain platforms and not others ... is there anything specific that you're concerned about?