Good Linux distributions, For a new computer! Options

[mipadi]

The time has come for me to purchase a new computer. I'm a long-time Mac user and planned on getting a Mac Pro, but the damn things are just too expensive, and as of now I'm looking at a Sun Ultra 24, which in terms of hardware is comparable to a Mac Pro, but much, much cheaper. It comes with Solaris, but I'm probably going to run Linux.

That's where you come in. I haven't dealt with the installation of Linux in a few years, and I'm not sure what distribution to use. Below are my prospects with my own comments, but any other comments are welcome.

For background: I'm a soon-to-be Ph.D. candidate in computer science. My "speciality" is computer simulation/computational science, so I'd like something that can do scientific simulation really well. Additionally, I'd like a computer that can do "the usual": surf the web, read email, listen to music, and watch the occasional movie.

• Fedora Core: I used this a few years ago. Didn't really like it. It's heavily geared towards servers and not the desktop, and its package management system sucks. Maybe it's gotten better?
• Debian: It looks cool, but I don't know much about it.
• Gentoo: My friends both run this. It's great -- except I'd have to compile a lot of software from source. Yuck.
• Ubuntu: It's okay, but not my favorite.
• Your distro suggestion here

This might be the wrong place to ask this question -- but any additional comments or suggestions?