The ECHL is a step down from playing in the Allsvenksan, and I simply don't agree that it is anywhere near the level of competition as the AHL.
I personally don't see anything wrong with him staying with AIK. He will without a doubt get top paring minutes and responsibilities there.
AHL or AIK. Either one is fine with me.
My honest preference order would be:
WHL
AIK
AHL
.
.
.
.
ECHL
It'd be stupid even to even think of sending him down there.
I'd like to see what he could do in the WHL. I mean, he'd be going to a good team, he'd definitely be able to show off that skill level. My second option would be for him just to go back to Sweden for a year. Get bigger, play lots of minutes. If he doesn't like his coach, etc, use some NHL pull and get him to team that would give him a ton of minutes. The good thing with European prospects, is you can stash them in Europe (like the NBA) and get them over here when they're nice and ready.
AHL would be a valid option, but it looks like we'll have a glut of talent there, that are further ahead on their development curves and need to be playing there. I mean, guys like Sieloff are nearing that make or break period, they need to be playing actual minutes (and not forward) and getting some reps.