Where do you think Haegon I and Bittersteel landed initially? The Vale, the Stormlands, or the Crownlands? What would be the pros and cons of each? I thought of the Reach too initially but the west coast seems awfully far for them and the GC to risk sailing. What do you think?

I doubt it’s the Vale, the Blackfyres never had much support there. 

If they’d landed in the Crownlands, or arguably even in the Stormlands, I think the Third Rebellion would have been much shorter than it was, as was the case in the Fourth Rebellion which began and ended with a single battle. 

So I actually like the idea of a landing in the Reach, despite the extra distance, especially if the Blackfyres thought they had naval support from the Greyjoys.