I'll throw in my two cents on this thread.
I just bought the Slash and had done some research between the AE SC10, Slash and the Desert Truck.
I weighed in parts availablility, reliability, design and what most people are racing.
The Slash uses new technology over the other two. Like the Planetary gear differential over the old ball type diff. Not that I can say that either have an performance advantage but the ball diff's definitely wear out. The Slash uses a similar designed tranny as that in the Revo and owning one of those, I raced weekly for two years and never had to take it out for any reason.
I pretty much so threw Losi out of the reliablility category. Everyone I know who owns one to race always have somekind of design flaw, poor quality plastics or whatever plagues that particular vehicle. For example the Losi Eight suffers from right rear hinge pins breaking and eats throttle servo's, (both supposedly corrected on the 2.0)
Then their is parts availablility, This is the biggie: unless you live in the middle of nowhere and always have to order parts, every hobbyshop will carry Traxxas parts and being the fact that the Slash is the hottest truck right now, the likelyhood is even greater. Some hobbyshops carry AE but you could easily find yourself out if you need a part right now owning an SC10.
Then there is the racing... Its called the "Slash" class, not the SC10 class or Dessert Truck class. So if you show up with an SC10 or Desert Truck wanting to race in the slash class, you may find yourself S.O.L.
The last question is how about performance? The SC10 is not out yet, so for all we know its a big bumbling turd. Didn't research the performance of the DT since I blew it off way back at reliability.
So that was how I looked at it. But its your choice. I am sure in the end there is no real dissapointment buying any three of those trucks but I just wanted to make the best choice for me.