For a WWII bolt action, the easy choice comes down to a decision between the Mosin Nagant or the k98K Mauser, and the cartridges for each, either the 7.62x54r or 8mm Mauser.
Both would be fine choices, and both do the job they were intended to do. Personally, I like the Mosin Nagant sights better as I feel the inverted V front sight on the Mauser is getting harder to see as I age. If you had to arm an army and couldn't (or wouldn't) spend time training said army, the Mosin Nagant wins with it's simple design and ability to be maintained with no tools required (firing pin depth could be "guess-ta-mated", using the tool is better of course!). The Mauser's bolt is more difficult to disassemble and reassemble, and the entire weapon requires more training (how to operate the three-position safety, etc.). With training, the Mauser would be my choice as the k98K is a very fine weapon (if a few years could be added to the selection, the Yugoslavian M48 is the most developed Mauser style rifle, with a bolt stop for an empty magazine, etc.).
To me, the k98K is the superior choice to the Mosin Nagant (and I love the Mosin Nagant!) with it's size being a huge factor in my choice. Shorter than the M91, and light enough to lug around while retaining enough weight to make shooting comfortable. Opening up the selection of Mosin Nagant models, the M38 model would rank high on my go-to list, being shorter and better to handle in an urban situation; but one needs to be ready for the stiff recoil of the M38 (learn how to shoulder the weapon correctly!).
Both the 7.62x54r and 8mm Mauser cartridges will do the job they were intended for, and ammo supply would be equal versus more exotic cartridges such as the 8x54r Mannlicher, the 7.5 Swiss or 7.5 French.
One rifle left out in the discussion thus far, which was an excellent weapon, is the British Lee Enfield with the .303 Brit cartridge. With 10 rounds in the magazine, very good sights on the Mk. 4 and an excellent cartridge, the Lee Enfield must be considered. The slickest action of the bunch, it again strikes a balance between weight and shooting comfort. Easy to load, simple to maintain and rugged, the Lee Enfield is different from the other choices, but must be considered as one of the pinnacles of development for the bolt-action rifle.
My all around choice of WWII bolt-actions? Lee Enfield Mk 4. hands down.