Alas, the search is over...After 2 months of downloading linux iso's, 6 weeks of partitioning hardrives, and countless hours of researching distribution bugs, anomalies, and querks...the answer is in: THERE IS NO "BEST" LINUX DISTRIBUTION....for hosting UnrealTournament/UT2003 servers
There are however some simple but important considerations you should make before selecting your" Linux distro. Practicality vs Simplicity is what you will most likely face in your decision.
First Stop: Let's start with the easy one: if you have a sparkling new 3ghz procesor, about a gig of RDRAM, and a 120gig serial ATA hardrive...STOP HERE!!! This info wont apply to you...simply load your favorite OS, SuSE, Redhat, (even WindowsXP) or whatever...then read all the instructions carefully for the UT server and have fun with it. After all, this is why you bought a nice new computer, ...isnt it?
Next stop: If you have a computer with a fairly modern processor (lets say PIII 1ghz+ or P4), a fair amout of RAM (512mb or more), and hard drive space is definately not an issue (lets say you got an extra 10gig-20gig laying around), ....then you may as well lean toward a more complete Linux distribution and enjoy a little more of what the wonderful world of Linux has to offer....where OS also stands for Open Source
SUSE and REDHAT are both highly commercial versions of Linux whose developers have gone to painstaking efforts to ensure that all the t's are crossed and the i's are dotted so that you can spend more time using the distribution and less time configuring it. MANDRAKE is also commercialized and very refined, but all other measurements aside, there is one huge thing that sets Mandrake apart from the other "major" distributions....ITS FREE!!!! Anything it loses to the other distro's it gains back with the extra padding in your pocket more suited for things like ....well, beer! hehehe. If money is not an object, then SuSE is my personal favorite. I give it the edge due to it's very easy installation and good assortment of tools to make upgrading a cinch. With one of these modern computers you can run the UT server from the X-Window GUI with no problems, and also have easy access to a file manager for ease of installation and a browser for admining the server. Optionally, you could run the server from a shell prompt (without starting an X-window session) to use less overhead if you have a less powerful computer, or if it is to be used as a dedicated server only.
The last stop: This brings us to somewhat older computer systems, and we now have to lean a little more toward simplicity and forgo all the bells and whistles. Now we're talking about a computer with less than 1ghz of processing power (preferably at least 400mhz), and at least 256 meg of RAM...if you dont have 256 meg of RAM, save your lunch money and just go buy some, it dirt cheap.
If your computer is toward the upper end of this catagory, then you might also consider the more popular distributions listed above, ....but starting with the installation, you should have as few unnecesary things loaded as possible. During the installation, select as few packages as possible and if it's an option, have it start as few service as possible at boot-up, and then elect to "not" start the X-window system automatically. You will also need to do a little research and manually turn off unnecesary servers at boot time like CUPS (for printing), WINE (for Windows enulation), FTP servers, Web servers, remote admin servers, and a host of others... This should keep your instalation lean enough for running a smooth UT server and yet still afford you the opportunity to utilize the benefits of the OS if you want to ...Bye the way, if you have an old MAC computer laying around collecting dust, you can get a PPC compliant version of Mandrake 9.1 and breath an "Unreal" amount of new life back into that old box, lol.
If your computer is not on the upper end of this scale, then you would be better off finding a distribution that's already lightweight "out of the box". A very important note to keep in mind is that the further you stray from the mainstream commercial distributions of Linux, the more you increase the likelyhood that you will run into some kind of an incompatability issue with your computer hardware. The best bet is to try 2 or 3 of them and see which distribution seems to work the best with your rig....In most cases the choice will be obvious. Additionally, be prepared to learn a little bit about the Linux OS and it's peculiarities. Although there are many distributions to choose from, very few of them have easy or even intuitive installations....but on a better note, nearly all of the distributions are totally free to download ....so those beers you bought with the money you saved, you might need them at some point during the Linux install, hehehe. Two of the best lightweight (and complete) Linux distributions I've found so far are VECTOR LINUX and PEANUT LINUX . Both of these get points for a fairly easy installation (compared to similar distributions), a complete set of software and tools for the average desktop user, they both run fast, and they both have a choice of X-windows GUI's to select from. Peanut comes loaded with KDE 3.1, which is the defacto standard for Linux X-windows GUI's, but I recommend disabling it when running a UT server. Although it has all the best goodies built-in, it also weighs in as the heaviest of all the X-windows GUI's...which will eat up resources on an already taxed computer. The current version of Vector Linux is in the RC-1 stage of developement, which means it is stable, but there are likely to be a few additions or refinements in the finished version, which is due out very soon. Vector Linux is based on Slackware, which is the oldest and considered to be the most stable distribution of Linux, and is very fast. So fast in fact, that the lightweight X-windows GUI can probably be run concurrent with the UT server and show no ill effects. Based on the stability and speed of Vector Linux, I would have to give it the official "nod" over other similar distributions, including Peanut Linux.
Here are a couple of great places to start in your search for the Linux that best suits your needs.... ibiblio.org and Distrowatch.com
A final note...for those who are not weak of heart and have already backed up all their important data. You can dual boot your Windows OS with a fast Linux distro, for those times when you want to run a clean UT server...it's not too difficult to set up, but it will require that you do a little research on the subject. Additionally, if you are limited to only running one copy of Windows XP, and your Linux installation will be on a second (or 3rd) computer, then you can just as easily dual boot two Linux distros....A nice full featured one like Mandrake, and a very fast and stable one like Vector. This way you will have the best of both worlds...the Real one and the Unreal one.
Best of luck with your new Linux OS and your new UT server, but most of all, I hope you keep on UT-ing