A few days ago I replaced Debian through ArchLinux on my Laptop. This is a big deal, because I use my Linux every day, and because I had (yeah, had) about 20 GB of important data. Important, that is no installed stuff, that's documents, personal data and rare files, something you can't just redownload.
That's also why I spent the week before with some really tedious work. Deleting and backing up. This is my proven strategy: delete everything you don't need and backup the rest. It did work out very well, and I'm very satisfied with my new Archlinux, without having important data lost on the way.
In that sense, I have some nice tools that helped me doing it right. First, there is Brasero, the best burning application a GNOME user can have. I used it to burn my important data to several CDs and DVDs. Brasero can verify the integrity of the burned data, which gave me a secure feeling when deleting my files after the backup. Then there is GParted, the GNOME Partition editor. It enabled me to repartition my HDD without losing the windows installation. Yes, it's possible with free software. Before trying GParted, I always thought this would need some really expensive piece of software, like Norton's PartitionMagic. Obviously it doesn't.
After these technical details, you may wonder why I did install Archlinux in the first place when I already had a working Debian installation? I don't know, I just wanted to try something new. But so far I think Archlinux is the better choice for me. It's faster, it has a better package manager and it allows for far more control. I won't go into the details now, but Archlinux seems to be better suited for Linux experts. You have to manually adjust quite a few aspects of the operating system, and it doesn't feature easy-to-use interactive assistants. Also, it's more suited for desktop use, and that may be one of the main reason why it simply "feels" better.