The best seat inthe house is the left seat farthest forward in the plane... but since that's likely already spoken for, I'd say it depends on the carrier.
All of the first classe seats are excellent, of course, and recline into nearly 'lay-flat' beds.
The Economy Plus section is the next choice. The seats have a few more inches of pitch (room between seats) and reclince somewhat more. If I'm riding in the back, I always opt for an aisle seat... not much to look out at at Fligh Level FL350 and above anyway, so I don't want to pinned gains the wall by Mr. or Mrs. Giganto in a window seat.
Always remember, most of the seats on most carriers just in front of any bulkhead (or rest rooms) do not recline, if that's important to you. Also remember that most of the carrier's aisle side arm rests will raise up if you know how to help with entering or eiting the seat row.