Macaron filling

...ganache sets harder but neither is very steady in hot room temperatures. It's purely a matter of which is best at delivering the flavour and texture you're after.

I've read some people use peanut butter. If you want a buttercream to hold up at a hot room temperature you gotta use shortening for part or all of the fat. If it's really hot, go with all hi-ratio shortening. Here are some great ideas: http://www.indulgewithmimi.com/macaron-filling-ideas/

Renowned macaronologist Pierre Herme frequently uses a white chocolate ganache with various flavoring agents, as a most basic rudiment, but also buttercreams.

I've never made macarons, but let's just say I've eaten a few in my time.  ;p

IMO, while buttercream and ganache are different, I don't have any real preference for either. If you do, then that's the way to go; your personal preference and those of the people for whom your baking are what truly matters. 

And there are lots of other things you could use that won't drip - other types of icing, stiff whipped cream, jellies, spreads that are thick enough, etc. You can also put things that would drip on their own if they're dabbed in the middle and encircled by a ring of something firm enough to hold them in.