devincutler
Explorer
My answer would be that it depends.
If you are a relatively new DM then the DMG hands down, as it has a lot of pages devoted to how to run a game. If you are an experienced DM, those pages are a waste (I am not complaining about that fact, but it's true nonetheless). That leaves the tables and alternate rules and magic items in the DMG.
If you intend to run your players through the premade official adventures (OotA, HotDQ, RoT, et al) then you may not even need the Monster Manual, depending upon which adventures you intend to run next. For example, HotDQ came out before the Monster Manual and so there are free online downloads of all of the monster stats needed for those, so you really don't need the Monster Manual or DMG for those.
If you are running your own scenarios or third party ones that don't have statistics, then I would recommend you get the Monster Manual first. You will be lacking alternate rules, but who cares at first? You are all learning the system. You will be lacking magic items, but 5th edition is supposed to be lite on magic items, so especially at first beyond low level spell scrolls, potions of healing (which are already in the PHB) and +1 weapons and armour, you should be covered anyways.
If you are a relatively new DM then the DMG hands down, as it has a lot of pages devoted to how to run a game. If you are an experienced DM, those pages are a waste (I am not complaining about that fact, but it's true nonetheless). That leaves the tables and alternate rules and magic items in the DMG.
If you intend to run your players through the premade official adventures (OotA, HotDQ, RoT, et al) then you may not even need the Monster Manual, depending upon which adventures you intend to run next. For example, HotDQ came out before the Monster Manual and so there are free online downloads of all of the monster stats needed for those, so you really don't need the Monster Manual or DMG for those.
If you are running your own scenarios or third party ones that don't have statistics, then I would recommend you get the Monster Manual first. You will be lacking alternate rules, but who cares at first? You are all learning the system. You will be lacking magic items, but 5th edition is supposed to be lite on magic items, so especially at first beyond low level spell scrolls, potions of healing (which are already in the PHB) and +1 weapons and armour, you should be covered anyways.