A tablet? Better make sure the notes are all online and aren't provided on paper. Those Fujitsu tablets are also extremely expensive. The Mac OS will never be attacked at the level that Windows is. The amount of malware on the Windows OS is growing at a staggering rate. Mac marketshare may rise, but it won't grow to any large proportion of the market. Windows a more secure OS? It is simply not. If that was the case, no antivirus or antispyware program would be required. Not that I have any issues with other computer vendors or Windows in general but I prefer Macs. The OP did in fact ask about which Mac to buy.
The fact remains that every OS has security holes and I would hope that Microsoft has a good security team to patch vulnerabilities when they are found. Despite the fact that you say that Apple must be extremely slow patching some vulnerabilities (obviously they are in some cases), but I don't plan on handing my computer or home network over to a hacker so they can try and steal my documents or information. That is where most of the vulnerabilities are and it would require physical access to my network. However, no amount of security can cure the problem of a user downloading and installing a trojan by giving their administrator password. Add that to pirating iWork or Adobe CS4 and you have social engineering at its best and one of the biggest trojans for Mac out there (not saying much however). Difference is that the countless viruses for Windows is that nothing can prevent a new virus from spreading before the antivirus companies even discover that it exists. There is nothing to stop it.
FYI I do enjoy the fact that you believe hackers will target the Mac OS because the users have what I'm assuming you mean either money in their bank accounts or credit limits on their credit cards. What you fail to realize is that creating a virus for Windows allows the hacker to make thousands of dollars a day by creating botnets. Plus, there are just a lot more Windows computers out there that are vulnerable to all kinds of attacks and a higher amount of money to be made. Not only that, but a virus spreads without user input. The only thing out there for Mac are trojans, and they require user input and cannot spread from user to user. How many trojans have there been in the history of Mac OS X?
Tell your friends who bootcamp all the time with their MBP that they are wasting their money. Though I have a feeling that you are exaggerating a bit. What are they doing on Windows? Video games? Tell them they got the wrong machine.
Last, your post wasn't a stereotypical pro-Windows post at all.