The police version has the standard M700 stock and the barrel is much slimer than the standard M700 barrel.
The diference between the M700, M40A1 and M24 is the stock.
Don't look at all at the Take Down versions , these pretty crap and even more inconsistent than the others.
Pre-ban versions have the PCS (power control system) but from what I've seen so far everyone adjust it to max and leave it there. Also if you run the gun with externally gas source like CO2 or HPA, PCS is practically useles cause you adjust the fps from the external rig (this solution gives you much better consistency)
The AICS as stated is an M700 in AI stock and it's the heavier of all. I had an AICS and sold it and I've kept the Police, it's much easier to skirmish with a lighter gun.
But I'd suggest to avoid gas guns cause all are very incosistent (unless you've rigged them externally).
And Tanaka are way overated!! They tend to break down fairly easy and spare parts are fairly difficult to track down.
Wolf