what kind of bullets do you recommend for the AR and ak-47
different bullets have different uses.
full metal jackets(also referred to as ball ammo) are generally used by military as they are easier to manufacture and a treat signed long ago pretty much made it illegal for militaries to make ammo designed to create gruesome injuries. it's normally the cheapest stuff around and is good enough for punching holes in paper but not much else.
then you have soft point, hollow hollow point and polymer tipped ammo designed to fragment, expand and otherwise create as much damage as possible. these are usually used as hunting ammunition.
depending on what you intend to do with the ammo is what determines the bullets used.
also is the ak-47s bullet bigger and stronger then the AR's bullet
I might be over simplifying here but the AK47 generally uses a 30 caliber round(3/tenths of an inch in diameter) while the AR15 normally uses a 22 caliber bullet(2.2 tenths of an inch in diameter). one advantage of the wider diameter is that the bullet can also have greater mass in the same length bullets. the average AR15 bullet is 55grains while the AK averages 123grains.
however the AR offers greater velocity and the lighter, thinner bullet loses velocity slower and is affected less by wind than the fatter, heavier and slower AK bullet. as a side effect the AR15 maintains more energy(calculated in pounds per foot or FTLBs) over greater distance.
at point blank range the 7.62x39mm(AK47) does have more energy than the 5.56x45mm(AR15) but over distance the 5.56 takes the lead.