They are two of the better weapons. If you are expecting mw2 style weapons later you are going to be disappointed. M16 is great at mid to long range, up close it sucks though because you generally need two bursts to kill with it. MP5K is the opposite, great hip firing at short distances but sucks at range. Choose the weapon best suited to the map and you'll be fine.
Besides you'll soon be able to buy the Enfield which is a great gun. I tend to suppress most of the assault rifles as it seems to help with the recoil.