Love this thread and even though Jaws is giving Polyaddict crap, I like knowing why!
This one is really hard, because for me it's looks plus personality and I don't know what LJ personalities are like yet, really.
I hate to jump on the PBB bandwagon but I would love one based on looks alone. They were one of the first on my "eventual wish list".
Also at the top of my list would be Faranah Lap.
I love my WC Del because she is an UJ but looks sort of LJish and she is very peaceful despite being the largest one in the tank.
But my Polli, though they are not the prettiest at adult size, is so dang active and personable that it would also be a strong contender. I like my fish to be visible, and in my heavily scaped tanks the Polli is #1.
Choosing ONLY one single fish though... if I think eventual 180+ gallon tank... I would be tempted for a LJ species because I think they are even more prehistoric/dinosaur looking than the UJs, and since they're larger generally they'd be more impressive and visible. So which LJ is attractive and active/interactive? You tell me.
That's my short answer.