Which antivirus is the most easy work and Inventor load quickly files?
At work (Win XP Pro 32-bit) we use Symantec, at home (Win 7 64-bit) I use Avast! Free Home Edition. In both cases, Inventor files are excluded from real-time scanning. Both work well with Inventor as far as I can tell. I routinely forget to disable virus scanning for installation and have had no trouble with either one-- it just takes longer to install.
Excluding Inventor files (.iam, .idw, .ipt at the very least) from real-time scanning is important since Inventor opens a lot of files for a large assembly drawing, for example, and the virus/malware threat from them is extremely low (~0).
The company I work for uses Windows Security Essentials. I don't notice any problems with CAD files and I don't believe anything had to be adjusted in WSE in order for it to ignore CAD files.
The place where I work however (on contract) uses McAfee. IRC, they had to set it up to ignore certain CAD file formats, others appeared not to be affected. I don't believe they had to do anything for Inventor related files but they had to adjust it in order for it to ignore NX related files.
We use AVG here. I couldn't figue out how to except certain file formats, so I had to exclude my whole workspaces. Other than that, though, it seems fine to me. I don't even use any anti-virus on my home PC. I just pay attention to where I go, and what I download. I do use an active script blocker in my home browser, however.