For the past 6 years I have been shooting a 300 WSM exclusively for big game hunting. I love mine! It has a titanium Remington action, a graphite wrapped bull barrel and weighs in at only 6.5 pounds scoped. It is ported and has a very light kick, in fact my wife has taken three animals with it. It is loud though with the porting...lol.
Here's my thought on the comparison between the two:
Ballistics: Nearly identical. There is not enough difference to decide on that factor. Both are plenty of gun for virtually any big game in North America. Since both are 30 caliber there is a wide range of bullets available for game from big bears to antelope. I personally shoot 165 grain bullets for everything from antelope to elk.
Recoil: I actually believe the WSM has lower recoil. My understanding is the WSM gets equivalent ballistics with about 10% powder due to a more efficient burn of the powder in the fatter case.
Capacity: Yes, the fatter cases may very well reduce you by one cartridge. Check the actual gun you are looking at for that factor.
Availability: I like to know my load and carry plenty of ammo where ever I am hunting. Great ammo with premium bullets is available for either one, from the big online hunting stores, or load your own.
Action: Short action with the WSM, give you some weight savings. I chose to WSM for the short action.
Accuracy: My 300 WSM will shoot 0.5" to 0.6" groups (at 100 yards) all day long, even with premium factory ammo.