I wouldn't suggest to anyone they start their Ayreon journey with The Human Equation or Into the Electric Castle, but that might be based on my personal feelings about those albums. 01 is my favorite, but that might be too much Ayreon for someone to make as their first experience, despite it being fairly representative of what Ayreon is all about.
I would agree with this. Even after 13 years, I still haven't super warmed up to 01011001, mostly because of it's large cast of 17 vocalists, but I do recognize that many fans do enjoy the album.
If length is an issue for a first-time listener, perhaps going into Into The Electric Castle, The Human Equation, or 01011001 might not be the BEST idea as each album is over 100 minutes long. The Theory Of Everything and The Source are both under 90 minutes long, and Transitus is just over 80, but I wouldn't suggest Transitus to a first-time listener, but The Source might be a good spot.
When I first discovered Ayreon, I started with ITEC and THE, mostly because THE was their latest album at the time, but I also dove into some of Arjen's other projects as well, like Star One, so there were a fair amount of albums under his belt, even by 2005.
Of course, you could also just go at it chronologically and start at the beginning with The Final Experiment, however, as discussed earlier, it's not one of his best albums, and I think it can sound a little dated, but it definitely shows where Arjen's idea for the project began, and it really only got better from there after the first two albums.
I think I'll give 01 a spin as I head to be tonight to see if I find it better this time around than I remember it, though I feel like I say that everytime I'm in the Ayreon mood and listen to that album.
-Marc.