Well....I know the AK family very well(including the its derivates) and I'm glad to give you some pieces of advice.
As you already said, the 5.45x39 is faster and more accurate; the 7,62x39 is powerfull but might be hard-to-control, heavier and slower.
When you have to choose your weapon of choice, you must take in consideration several factors:
-The range(Where/at what range are you going to use it)?Both calibers can be used at relatively great ranges (350+ m), with the proper sights/optics.I would choose the 7,62.
-Stopping power and penetration(How much and what kind of damage do you want to make?):The 5,45 can cause severe injures to the human body, it has not a relatively bad penetration level and the stopping power is quite good).The 7,62 is a beast, makes a relatively clean wound-but-greater hole in the target(It causes less damage to the body than the 5,45), but is has a higher penetration level(You can hit a target even if it hides behind a wall).The power of 7,62 knocks down almost anything.Again, I would choose the 7,62.
-Carrying the ammo(What quantity of ammo are you able to carry/are you going to use?)
With 5,45 you can carry more ammo.
-Recoil:By default, the 5,45 has less recoil and it's easier to control it, but with a proper stock (recoil-controlling(collapsible))and a good muzzle-break, you can achieve a good level of handling control even with the 7,62.
-Weapon size and lenght:A 7,62 rifle is slighty bigger,longer and heavier than the 5,45.Weight and lenght is not a problem for me.Again, I say 7,62.
Conclusion:
7,62 is a universal caliber,it can be used in any situation.
Personally, I suggest you some other members of the AK family:
-Zastava M70-The Yugo AK and one of the best(Maybe the best) AK derivate ever made.
-IMI Galil-Izraeli made.Nice rifle.
-AK 101/102/105-Originaly, only 101 & 102 were made for export(chambered in 5,56x45).But now, as far as I know, event he AK 105 is available(chambered in 5,45x39...it is the direct successor of the legendary AK 74)