What option is best for 3rd floor heating?

pweedith

For a quick breakdown:
-2 family home with 2 separate boilers (steam heat)
-2nd and 3rd floor are one unit
-3rd floor was converted from attic into a 425sqft master bedroom. Insulation is ok. Open layout. 
-when they converted the third floor there was no direct heat source put in. 
-I live in this unit currently but eventually do plan to rent it out within the next year or two. 

So basically, I need advice on what my best option for heating would be. I've had 4 considerations so far: running a pipe for another radiator, running a gas line for a vented wall furnace, installing a mini split, or putting in electric baseboards. 

I had 2 different people give me quotes on running a pipe for a radiator from the basement to the third floor and it's looking like it'll be $ which is far more than I expected. 

For those experts on here who know all the pros and cons of each heating type, what option sounds like it'll be best. Ideally I want to balance cost, effectiveness, longevity, and ease of maintenance as this will be a rental property. Feel free to throw out something else if I'm missing any other solid options.

Thanks!

pecmsg

Mini Split with elec baseboard back up is cheapest. Also gives the option of using the A/c if it does get too hot.