Rain water diverter - which roof to run it off

Hi everyone. I'm about to get a water butt kit with a rainwater diverter. However, before I install it, I would like some advice about which downpipe I should connect it to.

My house has a north and south facing roof with the apex in between. Should I place the diverter on the downpipe from the south facing roof (near trees which are only 2m high at the moment, but will grow to 4-5m tall), or should it be on the downpipe from the north facing roof (no trees, but less sunlight so more potential for moss)?

Thanks for any and all advice.