In my opinion, no comparison. The royer made mics that I had previously liked sound absolutlely boring (on loud electric guitars). Including 421's. Rocking high gain guitars are what I love my Royer the most on. Granted I don't have a bunch of super expensive LD coindensors with a huge beautiful room, but I do have a nice start
i.e...414's, KSM32's, 4050's, Blueberry, 451's, 609's, 421's, 57's, PL20 etc...
I have only gotten to play with the AEA mics in a limited capacity so I can't really say much. What I can say is that what other trusted people have told me has been awesome, my limited use was great as well. However, there were a couple factors involved in my purchasing the royer before the AEA (I say before because I still want one and its high on my list). First, I was under the impression that the AEA would be less likely to react to well to really high SPL situations. Second I was under the impression that the AEA may not actually be as "fragile" as older ribbon mics, that it wasn't quite as durable and "road worthy" as the Royer. I do tons of live shows and with bands that I enjoy, a lot of my studio toys end up at the gigs. The Royer is now one of those.
Also, I have had nothing but great things to say about the Royer, but I don't want people thinking that I see it as the "be all end all" of mics, or even of ribbon mics for that matter. For me though, nothing has consistantly sounded nearly as good on guitar cabs as the Royer and I believe that anyone that does a lot of electric guitar recording could highly benefit from and would not regret the purchase (no matter how hard you had to save) of a Royer ribbon mic. Also, I am in no way shape or form affiliated with Royer or related to anyone there