There are a few hundred distributions out there. There is no best distribution, it all depends on your use. Many people will prefer Mandraeke, Fedora, Ubuntu for the complete lack of prior experience needed, some like Gentoo or Slackware for the customisability, some like SuSe or Gentoo for their package management, there are varying reasons as to why you can like one ditro over another, so at the end of the day, it's just a personal preference
Here's a list of most of the linux distro's out there: AbulÉdu, Adamantix, ADIOS, AGNULA, AL-AMLUG, ALT, Amber, Ankur Bangla, Annvix, ANTEMIUM, APODIO, Arabbix, Arch, Ark, Asianux, ASLinux, ASPLinux, Astaro, Athene, Auditor, Aurora, Aurox, AUSTRUMI, Ayrsoft, B2D, Bayanihan, BeatrIX, Berry, BIG LINUX, BioBrew, Bioknoppix, blackPanther, BLAG, Blin, Buffalo, Burapha, ByzantineOS, Caixa Mágica, cAos, CCux, CDlinux, Censornet, CentOS, ClarkConnect, CLE, Clusterix, clusterKNOPPIX, Co-Create, Cobind, Condorux, Conectiva, Cosix, CRUX, Càtix, Damn Small, Danix, DARKSTAR, DeadCD, Debian, DebXPde, Deep-Water, Defender, DeLi, Devil, Dizinha, DNALinux, DragonFly, dyne:bolic, Eadem, eduKnoppix, EduLinux, eLearnix, ELX, EnGarde, ERPOSS, ESware, Euronode, Evinux, EzPlanet One, FAMELIX, Feather, Fedora, Fermi, Flash, Flonix, FoRK, FoX, FreeBSD, Freedows, Freeduc-Sup, Freeduc, FreeSBIE, Frugalware, FTOSX, GeeXboX, Gelecek, Gentoox, Gentoo, GEOLivre, Gibraltar, GNIX, Gnoppix, gNOX, gnuLinEx, GNUstep, GobLinX, GoboLinux, grml, Guadalinex, GuLIC-BSD, Haansoft, Hakin9, Hancom, Helix, Hikarunix, Hiweed, HKLPG, Holon, iBox, IDMS, Ignalum, Impi, IndLinux, INSERT, IPCop, JoLinux, Jollix, Julex, K-DEMar, K12LTSP, Kaella, Kalango, KANOTIX, Kinneret, Kate, kmLinux, knopILS, Knoppel, Knopperdisk, Knoppix 64, Knoppix STD, KnoppiXMAME, KNOPPIX, KnoppMyth, KnoSciences, KRUD, Kurumin, L.A.S, LAMPPIX, LBA-Linux, LFS, Libranet, LIIS, Linare, Lineox, LinEspa, Linpus, Linspire, LINUXO, Linux+ Live, Linux4all, LinuxConsole, LinuxTLE, Litrix, LiveCD Router, LiVux, LLGP, LNX-BBC, Loco, Lormalinux, Luit, Lunar, Lycoris, m0n0wall, Magic, Mandows, Mandrakelinux, MAX, MCNLive, Media Lab, Mediainlinux, MEPIS, Minislack, Miracle, MirOS, Mockup, MoLinux, Momonga, Monoppix, Morphix, MoviX, Munjoy, Murix, Mutagenix, Nasgaïa, Nature's, Navyn OS, NetBSD, Netwosix, Nitix, Novell, NuxOne, O-Net, Octoz, Omoikane, Onebase, OpenBSD, OpenLab, OpenNA, Openwall, Oralux, Overclockix, P!tux, PaiPix, ParallelKnoppix, Pardus, Parsix, PCLinuxOS, Peanut, Penguin Sleuth, Pequelin, Phayoune, PHLAK, PHP Sol, Pie Box, Pilot, Plamo, PLD, Progeny, Project dEv, Puppy, QiLinux, Quantian, Rays, Red Flag, Red Hat, redWall, Resala, RIP, Rocks Cluster, ROCK, ROOT, ROSLIMS, Rubyx, RUNT, Salvare, SAM, Santa Fe, Scientific, Securepoint, Sentry Firewall, Shabdix, Skolelinux, Slackware, SLAX, Slix, Slo-Tech, SME Server, SmoothWall, SoL, Solaris, Sorcerer, Source Mage, Specifix, SphinxOS, StartCom, stresslinux, STUX, SuliX, Sun JDS, SUSE, SystemRescue, T2, Tablix, Tao, TA, Tilix, tinysofa, TPM, TrianceOS, Trustix, TupiServer, Turbolinux, Turkix, Ubuntu, UHU-Linux, UserLinux, Ututo, Vector, Vidalinux, Vine, vnlinuxCD, White Box, WHoppix, WOMP!, WOW, X-evian, X/OS, Xandros, Xarnoppix, Xfld, Xteam, Yellow Dog, YES, Yoper, ZerahStar, Zen, ZoneCD