Lugia is by far the best physical or mixed wall in the Pokemon game. It is extremely hard to take down. It has a lot of advantages however, you have to be careful since it can be crippled by status moves and with its reliance on poison to deal with damage it can become the perfect Taunt bait. To make Lugia stand out and become more powerful it needs a partner. Once the partner is found and is compatible with Lugia it will certainly be the best wall.