Hmm, tough one.
For me, HM has the best ride experience – FJ is probably the best ride I have ever experienced. It can be a little ‘much’ at certain parts, (I tend to think I like ‘moderate’ thrill rides) but that makes it more exciting.
If you haven’t experienced FJ, you really need to try it. It is pretty stunning how they managed to theme it so well, and queueing in Hogwarts is an experience in itself.
The ride itself left me speechless. My now 8 year old nephew went on it, (he was 7 in October when we went) and he loved it. We then got my parents on it and they were impressed.
It isn’t necessarily too fast, or too frantic, and doesn’t have drops as such, it just moves you unexpectedly, and the animatronics are pretty much right in your face all of a sudden. I tend to think of it as a cross between a simulator like Soarin’ but more advanced, a lot more movement and more extreme, and a modern thrilling and extreme Haunted Mansion. It isn’t like a rollercoaster with big drops.
The HM area is fantastic; that was the first area we walked through. Immersive and impressive.
However, I must admit that the theming and immersion at DA is more advanced. I agree with other posters that you forget you are in Universal, which is incredible if you think about it. The dragon, the shops, the beer, the interactive elements, etc can all take up a lot of time.
Gringotts is equally as impressive inside. Queueing for this ride is again another impressive experience. I loved the bank, the animatronics, the lift, everything.
This ride, EFG, is like a cross between the Mummy and Transformers/Spiderman, but less extreme than the Mummy and more immersive and impressive compared to Transformers/Spiderman. It is like a moderate (some may say almost mild) coaster type experience but with incredibly immersive and modern simulator parts to it. I really did feel like I was underneath Gringotts and not in a theme park. I personally prefer theming and an immersive experience over full on drops and scary rollercoasters.
My mother was extremely impressed with all of it, and she does not know a lot about Harry Potter. To us, both areas had this feeling of a small and compact city like York in the UK.
Hogwarts Express is a must. You really need to try it both ways, but I personally preferred the journey from DA to HM.
I couldn’t choose between the two.
Good luck and enjoy.