Hey @crispincornett
Both Vundle & Vim-plug allow you to define the plugins you want to use in your vimrc, and then install via provided commands in Vim. This has the benefit that you can track the plugins in git in a very lightweight way. See the thoughtbot dotfiles vimrc.bundles file for an example. I really value having this list in git.
Pathogen expects you to take care of downloading the plugins into the ~/.vim/bundle/ directory manually.
Vim-plug has some additional enhancements around parallel installations as well as lazy loading plugins. Both sound great, and the author Junegunn Choi is extremely talented and prolific in the Vim plugin world, but I’ve yet to find it compelling enough to move away from Vundle. You can see a longer discussion in the thoughtbot dotfiles about moving to vim-plug