hmm, i wouldn't necessarily say that arch is more current. both arch and gentoo use rolling releases, and the gentoo community is still fairly active. what i might say instead is that the arch community has become quite active, and created a lot of new documentation whereas gentoo, whose documentation is still updated frequently, hasn't recently had any kind of redesign. but, it's still gentoo's stated goal to have the bleeding edge of the linux community development process, aside for possibly gnome3, which they've been actively masking out of the stable (and even dev) branches.
the real difference is that the predominant number of packages in gentoo are compiled specifically for one's machine based off of the specific set of use flags and package.use, and package.mask parameters, and relatively few precompiled binaries exist for gentoo. with arch, there are a lot more precompiled binaries and not having to compile everything from scratch (yes, i know you still can with arch, but this is not the default model) is more appealing to some.
all this said, i absolutely love emerge. arch's pacman is a very good package manager, but emerge is just amazing in my opinion. for someone just starting with a rolling release distro of linux, i'd say take a look at the documentation for both gentoo and arch and see which one you relate to more. after all, you'll be reading a LOT of documentation either way.