Depends on audience A5H, you are an experienced Linux user, you have setup Gentoo many of times and can walk someone through the Install blind, I can do the same with Arch, and while I would love Gentoo as my main system, I am a perfectionist and need to install multiple times before I even have my base, I dont even think I would be able to setup Gentoo with BTRFS easily, even with a guide, but I can with Arch.
For everyone else, here are good/bad points of both
Arch Linux Base (CLI Installer)
Good Points...
Stupidly light, Can offer similar builds via ABS, Yaourt for easy compile, Pacman and AUR is a massive database of things, Easier to setup than gentoo, A massive guide, stupidly easy kernel swap abilities,
Bad Points...
Been so light can leave you lost, ABS takes time to learn, Yaourt is easy but clumsy, Pacman and AUR are still not the biggest database, Not as easy as Manjaro .NET or something but you dont know whats happening then, Kernel swapping can be rocky as a bleeding edge distro, The forums are elitist forums Gentoos are a bit more friendly.
Gentoo Base (CLI Compile install)
Good Points...
Its built for your system only!, The database can compile anything for your system (Non binary so more performance) good guide, custom kernel at start, minimal footprint, faster than Arch unless heavily optimised and then its a challenge for Arch, Better community.
Bad Points...
Hard to setup for less savvy users, Documentation is no where near Arch Linux level (Although a lot of gentoo general fixes are found on Arch forums), Compiling can takes ages even if it doesnt stop you from working, the first install can take hours due to this, the distro is elitist compared to the forums if you dont know it your stuck, things like BTRFS and EFI can be a little bit more tricky to start, Partitioning of the drive is must know knowledge Arch can use scripts.
But at the end of the day, they both have good points, Arch can be setup in a rapid format, Gentoo can offer performance Arch could dream of, can achieve if you build it correctly, also binary packages are a good thing, someone has to provide for Ubuntu lol, yeah their compiling system is nothing compared to Gentoo/Arch
Arch is also a good stepping stone, you can learn vital skills from this to carry to gentoo, as said partition of drives, but to be honest schools should teach this stuff, Windows wont be here forever.
For now I shall personally stick to Arch, until I get the time to start a gentoo project and then I shall be calling on both Thirdmortal and A5Hs help lol, and maybe Zoltan and Brenn if they are ever about :)