I've been playing around with the two mod packs tekkit and Feed The Beast mod packs multiplayer wise. and i feel a big difference between them. Tekkit seems easier to understand at least for me and has a lot more "popular" i guess you could say. Feed the beast has some real potential though i think later on Feed the beast will surpass tekkit in user because of their respectfulness of the mod authors by actually paying the mod authors to let them use their mods. Plus the GUI in the menu has way more features like easily making your own mod packs and adding FTB to server is very quick and not advance as tekkit would be.