I judged Plateau Valley as the best Multi-player Arena Map after I performed some extensive testing on it prior to choosing it as the Arena Map for Valhalla's Tournament of Champions.
After more than 1700-hours in the BattleTech Beta I was very familiar with many, many corners of the Initial load of maps. Then at Launch I tested out the new maps and in time came to the decision that Plateau Valley was to me, the best Multi-player Arena Map in BATTLETECH.
Plateau Valley is a relatively compact map, with both players near to the map's edges and a significant piece of high ground separating them.
Like in the UFC, there is a material advantage to the player who advances into the center of the map ~ Elevation and potentiall its bonus "to hit."
While there are lines of cliff-faces on Plateau Valley, they largely serve to channelize movement while not effecting Line of Sight, something I found to be a surprisingly pleasant and pleasing tactical nuance.
Plateau Valley has none of the Extremely Restrictive Terrain that other Maps have proven to hold. While Jump Jets offer a marked and valuable advantage for the tonnage they cost and Heat they produce, Plateau Valley does not offer Jump-capable Mechs veritable #SanctuaryGround like BATTLETECH's Dessert Map withis it's High Mesa and attendant low ground.
All in all, I found Plateau Valley to be the best Arena Map from among BATTLETECH's Launch selection of Maps.
While I hope HBS_CaptKerberos and Team HBS may one day provide true Solaris VII Gaming Arenas, until such a time as that might happen, Plateau Valley is my selection as Best Arena Map in BATTLETECH. : )