Why would you want to make the base font smaller that the default 16px in the first place?

Hello world. This is 16 pixels. Looks fine to me. This looks to big to many web designers for a base font size.

Hello world. This is 14 pixels

Fonts look smaller on Macs

Pixels

Pros:

Are you kidding me! We use pixels for every other measurement, div widths, padding, margins etc if we are not making an elastic page, which mostly these days we're not. See siteinspire, css beaty, and the css awards and you won't find many elastic designs.

Cons:

If it wasn't for that pesky IE 6, we'd be using pixels. Who uses / supports IE 6 anymore. Oh and before you say well lot's of corporates..., how many sight impaired use IE 6 these days? If they they are, what the hell are they doing!

From IE 7 onwards, you can resize the fonts and everything else on the page by using the zoom function Ctrl + +. Unlike text only resizing zoom magnifies the entire page images movies buttons the lot. Surely that's a much better experience for a partially sighted person that just increasing the text.

Ems and the 62.5 trick for people who want simple maths ( that's everyone )

Pros:

Cons:

Rems

Pros:

Cons:

Ems with slightly more harder maths much lower maintenace

Pros:

No inheritance issues

Declare font sizes for exceptions only

Cons:

Pixel defined fonts don't scale up on IE6

The problem with this technique is the cascade