Avantasia has great Power Metal, Speed songs. Includes many great vocalists and some special surprises, Klaus Meine. I don't have Mystery of Time, so can't judge that. The first 2 albums are great as well.
Ayreon is my choice. I like the Grand concept of the albums, The Source is a nice prequel for 01, and makes me feel some of the characters from The Source are in 01 as well. Just by the tone in their voices.