Having owned and reloaded extensively for both- the WSM gives a few more fps, and MUCH less case trimming, particularly at loads near the top of the book. Perhaps better case life as well.
The 30'06 gives one or more extra rounds in the magazine, generally better feeding, and better ammo availability if you loose yours on a trip.
The extra velocity with the WSM is nice but does not give any real advantage until ranges get out past 400 yards- the same reason the 300 H&H was an advantage over the '06 long ago
If I had only one custom rifle it would be a 30'06.
