The 1st gen 4runner arms that I posted in response to that other guy above is actually a true J-arm upper and has the uniball integrated to the upper arm in the orientation you show. Additionally I have a 3rd gen design I've been slowly working on that I call the gen 2 that is very similar to what you posted and utilizes a fully fabricated spindle with 4th gen unit bearings and uniballs in that orientation.

The uniball best reacts loads radially through the race. The uniball being on its side (in regards to the bolt) is mostly advantageous on the top since the top arm is usually shorter and needs more angle capability than the lower. Since the upper has relatively low loads and is only reacting frontal and radial loads at the hub (ie not holding up the truck) it's less critical the orientation of the joint. The lower joint being the more heavily loaded of the two has more argument of the best joint orientation. With that said there are lots of vehicles that run the joint horizontally on the top and the bottom (specifically Ultra4s) where hub frontal loads would be reacted axially in the bolt direction, and plenty that run it vertically (trophy trucks) where vertical suspension loads are reacted through the bolt. Uniballs have lots of load capability in every direction (minus pulling towards the c clip) so maybe it's a moot argument either way, and probably more important to just optimize which way you'd rather not be angle limited---which again is why most uppers at least have the bolt horizontally, since the suspension travel would be limited far more than the steering would be limited.