Both.
I almost always use a 1.8 ohm boge carto on my REO mini. As to why: The carto adds a ml to the capacity - 1.8 ohm is a good compromise between vapor warmth and battery life (the reo mini uses a 14500) - and I like the flavor from the boge cartos.
When I have a serious craving, though, I put a 1.8 or 2.0 ohm 306 on for a few drags. Sometimes nothing else satisfies. A 306 with a drip tip on it plus a 14500 fits in a AA battery box, so when carrying the REO mini, all I have to carry is one AA box to have an atty and spare battery with me.
When I was using an old goat feeder, I either used a 1.8 ohm boge carto or or sometimes a 1.8 ohm cisco 510 atty.
On my VV feeders it's a little different. I've only had my VV REO Woodville for a few days. I did put a carto on it one day, but I don't know if I'll do that very often. Myabe sometimes when I'm cleaning attys. My VV Feeders are all about performance. I use nothing but an hh.357 on my VVPV and as soon as the 306 on my VV Woodville dies, that PV will get an i06 and that's probably all that will ever be on it.