There is a huge difference between using milestone levels or experience points to measure your D&D success. Having played both at this point, I can say that I prefer milestone. It just takes the pressure off of keeping track of the points. That isn’t to say that experience points aren’t fun.
Our first campaign was played using milestone but our second was played with survival in mind and we use xp points to measure our levels. Milestone is stress free. There is no need for the player to do much calculation. The DM/GM simple decides when it feels as if the party or a specific player has leveled up. Milestone level ups usually occur after the completion of an important story plot or a personal achievement in the game. They have meaning because they are the fruit of the hard labor of an adventurer.
Milestone is awesome but the drawback is that the player has no real control over their own leveling. They have to wait until an important quest comes up and the DM/GM gives them the opportunity to gain a level. This takes a bit of player autonomy out of the game. It also puts a lot of the pressure on the DM/GM to space out the levels in a way that is natural and makes sense to the story.
Experience based gameplay is a little more complex. I liked using it because it gave me more control over how my character leveled up. I also got to track my progress and see a physical representation of that progress. It felt a lot more involved and interactive. We had players decide to commit certain evil acts and gain a lot of xp others couldn’t. We had experience come from saving people too. The point is that we had a lot more control over how and why we leveled up.
XP points also have their own drawbacks. Even using a website to track my player progress proved to be a hassle. I would sometimes lose my progress if I hit the wrong button. I had to update my xp points but also go into the building system to change levels and update the numbers. It kind of took the fun out of the experience. Still, I was happy to have played both ways. I also think that we needed to play the second campaign with xp points to drive home the added difficulty that our DM wanted us to experience.
It was worth it to try both. I found out that I prefer Milestone based games but that doesn’t mean that experience based gameplay is bad. It has its place in the game. You just have to find out if you prefer control over your game or a game free of that pressure. As always remember to enjoy yourself and have fun.