I run a Gravity Dropper and I find when it gets to the point that I need to use it I want both hand on the bars not reaching round my balls looking for a lever, so I have a bar mount. However its a pain transporting if you have to remove your seatpost as there's always the cable attached to the post.
Personally I wouldn't bother with one with a lever.
I don't have either but where I've seen other people use them usefully it's been on the fly. For that I'd want bar mount. Otherwise Why not just stop and drop the saddle.
I have just upgraded my lever to a remote and it has made a huge difference. Sometimes your are flat out down a rough track with drops and jumps and rely on 2 hands on the bars.
Then you aint got time to pull the lever with any hand as its holding on for dear life
I would recomend everyone who wants a speedball to get a remote version.