There are two things you should be aware of before getting either a Saiga or CAI ak-74
-The Saiga cannot take high-capacity magazines unless you drill a hole for a bullet guide and install it yourself. It's easy if you have a mini-mill or access to a machine shop, and it's very inexpensive. You dont have to modify the magazine well.
-The Saiga barrel is not threaded. So if you want any muzzle break, you will have to thread the barrel yourself or install a new FSB with 24mm threads.
-I think you will have to install a bunch of new parts on the Saiga if you convert it to accept hi-cap magazines because, AFAIK, the Saiga is imported as is from Russia because, as far as the ATF is concerned, it is a "sporter" rifle that isn't suitable for defensive use. So you might have to do a lot more work than just install the bullet guide.
Regarding the CAI, be aware that the barrel is not chrome lined. This means 2 things
1: You absolutely will have to clean the gun within hours of shooting corrosive ammo. This is actually the same for the Saiga because the gas tube, piston, and bolt carrier will start to rust within hours, but in the CAI, the barrel will also start to rust within hours.
2: The barrel on the CAI is not chrome-lined. This will mean that accuracy will degrade significantly faster than on the Saiga as the throat erodes. Many owners of 5.45 rifles have found that the throats on their rifles are corroding after less than a thousand rounds. Others have said that their rifles last thousands of rounds. Throat erosion leads to a slight loss in accuracy AFAIK, but otherwise functionality is not affected.
If you aren't mechanically inclined, get the CAI and remember to clean your gun with windex or hot soapy water if you shoot corrosive, or just buy silver bear 5.45. It's actually about as cheap as wolf or golden tiger 7.62x39