Upper deck of the a380 in Y should always win out. Side bins for window seats create much more space (no bins on bulkheads). Some folks like the small 4 row Y cabin right at the back. Jet bridge attaches to the upper deck first, so you'll likely get off the plane a bit faster.

Lower desk a380 is 10 across on a 11 or 8 row cabin vs 10 across on a 13 row 747. IMHO take every opportunity to sit in neither.

I understand (tho don't agree) with the folks nostalgic for the 747, yes upstairs is great, yes, the nose has cool views and no foot traffic in row 1. But otherwise, would you prefer to go for a long drive in a 2 year old car with new seats and good air or a 20 year old car, albeit refurbished?