boiler heating or mini split in apartment building?

[Amy Hu]

I bought an old apartment building in OH, 17 units. Hired the wrong contractor to rehab, big mistake! The boiler was all rusted. That contractor installed electricity heating in the 12 units in the front building. It's not very efficient. Basically a fan look heater built in the wall in each room. I'm afraid the electricity bill in winter will be so high that tenants would just leave.

I consulted 2 HVAC contractors. One suggests converting into mini splits for reasons 

1. units already wired for electricity heating and lots of work have been done

2. mini splits are more energy efficient than current system

3. it provides air conditioning in summer which would be attractive to tenants

Another suggests going back to boiler because electricity is just too expensive. The problem is we don't know the conditon of the loop pipe for heating in the building. The only way to know if pipes are leaking is to run water through them.

I'd appreciate if you could share your thoughts! thanks