744/3-cabin/F class
As a solo traveler, I recommend 1A or 1K for privacy and a more spacious feel. Sure the closet in front gets some use, but that's really only during boarding and deplanning. I like to use the closet for storage instead of fighting for limited and inconvenient bin space over row 2.

744/2-cabin/J class
While the majority seem to prefer the upper deck, I'm a fan of row 1 for the room and the real potential for an unoccupied seat next to you.

A380/3-cabin/F class
Having just completed my first trip (where I was seated in 1A), I must say I definitely would recommend the "A" seats for solo travelers and rows 2 or 3. Row 1 seemed to get some continuing annoying activity in the storage areas right in front of the seat (where the closets are located and where the "body bags" containing the sheepskin mattresses, duvets, sheets, and pillows are stored). Also, crew members tended to congregate in the areas by the bathroom, and even though the curtain was drawn, I was able to hear the activity.