I have had a male of all three species mentioned.
Jacksons: Very timid, yet very friendly demeanor. He would shy away from being handled, generally by trying to hide from your hand. Once picked up would generally be calm. He never once hissed at me. He always readily hand-fed. When I came home from work, he would come down from his basking spot and wait by the entrance of his cage for me to feed him. It was so adorable. It seemed like he was always hanging out somewhere different in his cage. Never slept in the same spot twice.
Veiled: I don't have anything much to add beyond what's been said. He was tolerant of others until he was approximately 8 months old, and then quickly became extremely territorial. While a Jacksons will attempt to avoid being handled by hiding, the Veiled would simply try to intimidate you from trying. I never was bitten, but I think that's just from being experienced and careful. He'd have bitten me if I gave him the opportunity. Never hand-fed after 6 months old. I don't see them as being particularly active either. They tend to pick a lounging spot, a basking spot, and a feeding spot. Then they sit there and get comfortable and lounge there all day.
Panther: Very similar to the Jacksons. Is not quite as timid though. If upset, he'd gape at you, but would never actually try to bite. Most times would tolerate being picked up when necessary. Readily hand-fed up until he was about 8 months old, and then abruptly stopped. When he was about 10-11 months old my wife acclimated him to hand-feeding again and he hand-fed for the rest of his life. He tended to be pretty active. He would explore his cage quite a bit. He did have favorite sleeping spots though. He'd pick a spot to sleep in, and every night that's where he'd be. Then once in awhile he'd change his mind and pick a different spot, but usually his sleeping spot wouldn't change until I cleaned his cage and his plant got shifted around on him. When people approached the cage to look at him, he tended to be very calm. He wouldn't puff out and hiss like a Veiled, and he wouldn't try to hide like a Jacksons. He'd just sort of look at you, and check you out while you were checking him out. When I had the rehearsal dinner for my wedding at my house, his room was pretty crowded. I tried hand-feeding him with about a dozen people crowded around his cage, and he was absolutely fine with it. I was actually really surprised.
I've got a soft spot for Jacksons, but I love Panthers.