I have played both and in the end bought the Electra Dyne, but that is just my preference. I was strongly considering the Stilletto, if for nothing else then the crunch tone which is awesome.
The Stilletto is a much brighter amp then the ED. I think the Stiletto will get you closer to AC/DC then the ED will.
The ED is much thicker and has a lot more low end. It does the 80's Metal perfectly. Sounds a lot like a boosted JCM 800 The clean is amazing (clean on the Stiletto is excellent as well).
Stiletto has more gain on tap. But the ED has plenty. It is the first Mesa I have ever played on were you can max the gain and still have a usable articulate tone.
While I think it ventures into metal teritory and have no doubt it could do modern metal easily with a pedal, I think it is geared more towards hard rock. I play Metallica on mine, but my Mark IV sounds better playing Metallica (Go figure since they used Mark series amps). I would tend to agree with the other poster about it not doing metal if you are speaking strictly modern metal and no pedal. Definately more of a vintage vibe. But it will definately do modern hard rock
I think the Stiletto in crunch actually does the old Marshall sound better then the ED does.
For me I was just giddy after a few notes of first playing on the ED. Every other amp I tried, I may have liked a lot of things but there was always one thing that would annoy me.
Not so with the ED. It just blew me away. I was floored by it. Nice thick tight distortion. The low gain setting was awesome for your regular rock stuff ala Tom Petty.
The clean, you could setup for chimey cleans, or could push it and get sweet breakup.