Differences between wheelsets - 700c gravel bike and 29" mountain bike I'd like to set up my Surly Ogre for commuting. It currently has 29" 29mm internal width rims, for bikepacking.

I'm thinking of getting a second wheelset for commuting, so it rides less like a tractor. I've been looking at 700c gravel bike wheels or 29" mountain bike wheels, with an internal width around 19mm...

What would be the differences/benefits of these options? They each seem suitable. It seems like I could get either with hub spacing to fit the bike (100m front, 135mm rear). Strength?

I'd probably get a tyre like the WTB Expanse (32mm).

Example of 700c

Thanks
As comments to the question state, in terms of wheel diameter alone, 29" and 700c monikers indicate the same rim diameter. Your bike, being Surly, should be able to fit just about anything in terms of wheel diameters and tire widths, up to 27.5"×3.0" (650C) and 29"×2.6" (700c).

However, according to the frame specifications of the latest Ogre model, the frame uses "Gnot-Boost" 145mm spacing for rear wheel. It means it is compatible with  through-axle hubs of 142 mm and 148 mm widths, but not with 135 mm ones with quick release. There are adapter washers for QR wheels from Surly to accommodate for QR hubs, so it should be possible to use such wheels. I think you might also have to adjust the rear disc brake caliper position when axle type is changed, but that is usually required anyway at wheel swaps.

The bike does not have a front derailleur by default, but if you use one, the specifications page mention that you will have to use different derailleur offset adapters to keep optimal chainline.