This question is a tricky one.
Based purely on the artistic impression, I would say Millennium first (beautiful picture and music, it's hard to beat), Millenium 2 (closely) second and Dreamscape third.
But for me, title screen isn't only about "artistic impression", it's more like some kind of an intro to the game. If the title screen (and title music) is good, then I usually just sit there in front of the screen and try to "get the feeling of the game" before I actually start playing it.
This "staring at the title screen" is quite a special moment to me. No more looking forward to the game and guessing the plot, I have the game in my hands. And suddenly, I'm hesitant to start. Because once I start playing, I will eventually finish the game and then there will be no more surprises for me. I kinda feel as a small child unwrapping a gift sometimes, and that's why title screens are important to me.
All the Aldorlea games have good and fitting title screens and music: Asguaard is a bit cold and evokes feeling of a long road, Dreamscape feels dreamy, Millennium quite fairy-tal-ish, Laxius Force heroic and 3 Stars of Destiny reminds me of Outer World. If I should rank title screens according to this "overall feeling", I would place LF1 first (after all the anxious waiting, sequel to LP3 was finally on my screen), LF3 second (well, it's just LF3, that's more than enough reason for me) and Asguaard third.