Option 2 permits bulk deals on regular maintenance & replacement & may wind up more cost effective for all owners in the long run. Even easier if all the air cons are all the same model/manufacturer. Regular maintenance may prevent issues down the track e.g. with noise & air con related water leaks.
I’d be approaching a few air con maintenance folk & getting the actual cost of a regular maintenance/replacement schedule before making a decision. If the air con folk are on site for all units then at the very least you’re going to save on call out fees.