Archer, I'd say a combination.
Issue airsoft to the officers. The aggressors can wear normal clothing, with eye protection.
Issue paintball guns for the aggressors. The officers wear full protective gear.
And for your building clearing and active shooter exercises, people are important as well. If you want to get the best training possible, find about three or four Infantrymen or Marines. Tell them don't go easy, either.
The more you sweat in peace, the less you'll bleed in combat.
Hiding in plain sight...