I'm running the Lost Mine of Phandelver module with my players, and I've been using monster and reward XP as the book says so far. I have 5 players and they're all level 2 and have just cleared the Cragmaw Hideout.
However, I've been throwing in quite a bit of homebrew stuff I made, new plot points and enemies. I don't want to throw the level balance included in the base module away though. I'd rather stay with it so that I don't need to worry about balancing the encounters too much and I can base the difficulty of the stuff I add on what they're currently doing in the story.
I'm thinking of going with the milestone leveling system, so that they're all at level 5 by the time we're at the finale of the story. The book only seems to call one quest/dungeon as a milestone and that's the Hideout.
What other dungeons, quests, or story points in the module would make suitable level-up milestones to give them the level ups they need?