<IMHO>
Stecyl LOOKS more polished to me (even with all this mess in UI, i mean polished graphics);
It runs on wide range of platforms;
It WILL support HTML5 in the future (well, as said officially);
The game creating process seems more fluent, instead of Scirra's.
The difference between Construct 2 and Stency is that Stencyl gives community what they demand right now (step-by-step in every direction), while Construct is growing in one direction (with huge step), then in another (another huge step).
But I love Construct for better UI, for "no Flash" reason, for pricing system (though I dont want it to be cheap, cause there's no subscription, so no community growing - no money for devs).
</IMHO>