I have both a small and a large WSM. The BGE is a great, high quality product, but comparing a BGE to a WSM is really comparing apples to oranges.
For me, the important factors were:
Capacity - An xlarge BGE is about the same diameter as an 22 1/2" WSM, a large BGE an 18 1/2" WSM. The WSM has two cooking grates/levels so it has twice the cooking capacity of the same diameter BGE.
Cost - A BGE is 2-3 times the price of the same diameter WSM.
Weight - A BGE is a heavy piece, moving it around, even with wheels, is problematic.
For smoking traditional cuts of BBQ meat, at temperatures from 225F-350F, IMHO, the WSM is the way to go.
Bob