I am using Kaspersky 6.0 for Windows Workstation in Kaspersky Security Space suit. I think that is a best choice (my opinion).
I use the free one from Sophos but it's Mac only. It works well and doesn't slow down my computer, what more could you ask for?
Same here... For me I think MSE is the greatest FREE anti virus ever. Currently we are running MSE with more than 200 work stations for almost a year now and no worst problem we encounter related to viruses or malwares. I am not really a MS fan but MSE is really an exception, well next to XP service pack III
If you are using it on more than 15 workstations in a corporate/business environment you are breaking the Terms of use . What makes all of you think one is better than the other...... do you even know how they work and how they protect you?