For noobs: Macbook Pro 13 inch.
Pros: Go with the PC.
I have an MBP and a PC (HP Envy 15). I love em both. Both are extremely useful but pick up the Macbook first. It's zero maintenance and easy to use, it will help you get organized and hassle free.
The HP Envy is a piece of crap, some of the buttons don't work, the trackpad is really shitty, changing the volume either doesn't work and kicks you out of full screen applications. I had to spend about an hour just going through 3rd party forums, downloading fixes and messing with the configurations. The battery life last less than an hour on a good day. However, 2 things make it better for IM: Windows 7 and its power. The Envy configuration that I have (Intel i7, 8gb ram) is key to be quick enough and run intensive applications. Both laptops cost the same and to get that configuration on a MacBook would cost you thousands more. Mac OSx isn't as effective in my book, but maybe that's because I grew up on Windows and know it better.