Personally, I love Ubuntu!!!
My main laptop is a Mac, but my baby laptop is Linux...I've tried soooooo many different distros and of all for me, Ubuntu is the best!!! Far better then Windows 7, especially the most recent version of Ubuntu
(I use Windows 7 on my Mum's laptop, and find it pretty buggy)
Really though it's all down to personally preference - the best thing to do is make a live USB bootable stick version of different distros using a 4GB memory stick, when you turn on your laptop, instead of booting from the hard drive, boot from the stick instead and you get to try the different OS without it removing anything from your system
I wouldn't remove Windows 7, but when you find the OS you want you should create a partition and install the new OS, so that you have the two on the same laptop, that way you can change between them. (It wont slow down your laptop)
It'll show you how to make the live USB stick on the link above via the 'download' button (use a free software called uNetbootin to make the drive - it's very easy!!)