1. The safety on the Yugo AK has a tab to make it easier to flip up and down, while the WASR10 has a typical AKM safety
2. both of these receivers have an "S" and "F" (many collectors wouldn't buy either of these because of this) some of the better quality US made receivers have no selector markings 
3. The WASR-10 has import information scribbled on the side. Usually this is difficult to read because it's so sloppy. The US made Yugo receiver has nothing written on this side (except the large selector markings) 
4. The rear sight lock button is different, might be hard to see, but the Yugo Ak47 has a more finely built part
5. Note the shape of the upper handguard / gas tube lock. Neither is better, just made differently

A view of both sides of the pistol grips and rear of the receivers. The obvious difference in he Yugo underfolder stock. You can easily see the many differences in the rivets and there are large holes for the underfolder mechanism . The rear sling mount on the Yugo is on top of the button used to close the underfolding stock

1. These two use very different receivers. They also have different front trunnions. The Yugo Ak47 Underfolder (and most other Yugo AKs) use the RPK trunnion and receiver. The RPK is a much larger rifle and it's receiver is half again as thick as a typical AKM receiver.
2. Both of these receivers have writing on the sides. The Yugo receiver has much less writing and it's done very precisely so it remains small. The WASR10 has larger writing up front
3. The WASR-10 has no dimple...
4. The Yugo has no soviet optical sight plat. The WASR-10 does come with this sight base plate installed. This allows the shooter to add a soviet style scope or an optics mount for other scopes that are anchored to the receiver. Most agree this is the best option if you are going to mount an optic on an AK 
5. The pistol grip on the Yugo Underfolder is the typical Yugo plastic pistol grip. The Yugo pistol grip has a contoured area at the back to fit the hand better. 

1. The Yugo Underfolder (like other Yugos and RPKs) has a lock on the receiver cover, the WASR-10 (like most AKMs) has no lock 
2. the Shape of the safety levers. Note where they ride on the receiver is different on each. Note the fit on the factory  made AK (WASR-10) and the Yugo (built in the US).
3. The safety stops are different on each AK.
4.  The selector markings and the safety selector stop are very different on most AK47s and US made receivers.
5. The shape of the hand guards on Yugo AKs are usually quite straight, where other AKMs use more curved shapes. Also note the WASR-10 is made from plywood while the Yugo is solid wood

1. Note the quality and finish of the smaller parts. Typically an advantage of a factory built rifle is the factory finish
2.The fit on this WASR-10 is good (not always the case) while the US made Yugo is missing a piece of the lower handguard. Watch this are on AKs you might buy, a poor builder can have quite a bit of slop there.
3. Note the different shapes of the front trunnion, neither is better, just different
4. where the receiver cover and front sight block meet. Another place to check for quality of manufacture. An AK47 may be sloppy, but large gaps can be an indication of a poor build. This US made Yugo has a sloppy match to the sight block, while the factory WASR-10 happens to fit well (not always the case)
5. Shape of the top receiver cover. Aside from the lack of strengthening ridges (like an AKM) the thicker Yugo receiver cover is also cut to a slightly different shape

1. Note the slightly different shape of the charging handle. of course the Yugo Underfolder (and most Yugos and Chinese) has a polished bolt carrier, the WASR-10 (like most AKMs) has a dark bolt carrier
2. The front handguards are shaped differently, and the WASR10 is made of plywood.
3. The two have different places to attach the sling. The WASR has a sling mount to the rear on the handguard retaining lock, while the Yugo Underfolder has it's front sling mount on the gas block with the bayonet lug
4 Note the slightly different shape of the bayonet lug. Both can use each others bayonet however, there is no affect on usage between these shapes
5. The barrels are slightly different lengths, their front sight blocks are different and even the slant breaks are slightly different

A few more views of the front ends of these two AKMs Note the slant breaks, sling mounts and bayonet lugs

1. These both use a slanted gas block, some other AK47s and AK74s use a gas block at a right angle or 90* (ninety degrees)
2. These two have quite different front sight blocks. The Yugo Underfolder has a night sight option while the WASR10 is a standard front sight
3 The WASR 10 has handguards made of plywood, so a pin is inserted to keep the wood layers together, these pins are also visible on stocks
4. The Yugo Underfolder has the ability to launch grenades, so there is a grenade sight and gas shut off on it's gas block.

More views of the front sights and gas blocks of these two AK47s

Views of the front sights and gas blocks (grenade launcher) from above

The front sights with the night sights up (open) and down (closed) these have expired and been removed or painted over. Many Yugo owners will paint hi-visability pain on this old night sight for a similar effect

1 differences in the size and shape of the front sight blocks
2. the Rear Sights and the Yugo flip up Night Sight 
3. The shape of the charging handle (the Yugo is bright metal, the WASR is dark)

1. Tool marks on the more crude WASR-10
2. The bright metal changing handle and bolt carrier on the Yugo
3. The AKM receiver cover on the WASR-10 vs the AK47 style receiver cover on the Yugo Underfolder 
4. The Yugo flip down night sight on the rear sight
5. Note the differences in he sight markings. Both go to 10 but they have a differently written "10" some AKs have other languages written on the sights or different distances (range increments)

Larger details like the number of holes between the upper and lower front handguards (three on Yugos) the Pistol grip and the style of stock might be easier to see. but the details are better clues to the quality of the build.