how important are you?
that's the best defence you can have
every machine is vulnerable in some way ... the linux and mac brigades bang on about how safe they are ... it's not that their OSs are superior (in fact ... look on the serious security sites ...
you'll see both have many many more vulnerabilities than any version of windows) ... it's just there are so few of them in the scheme of things they're not worth the effort.
you are relatively safe accessing an https address ... but your machine is full of holes
copy you credit card number to paste into a page ... and it's not protected - quite simple code in a web page can access your clipboard.
http://www.paraesthesia.com/archive/2005/01/20 /ie-users-javascript-can-access-your-clipboard .aspx#
the worst vulnerability is stupid people
your bank account will be suspended unless ....
and 100s of idiots log into a phishing site with their id and passwords...
send an e-mail that says I love you .... and even hermits will open the mail to see who .....
there is no such thing as safest ... what you are looking for is most obscure.
either that or a company who will plug a hole within hours of it being reported and updaye your machine with the fix ....