Of the standard package plains game the Kudu has to rank as the most stunning, they always catch my attention. When you see them in the wild they are even more impressive. Really not that hard to hunt, I saw lots of them. Elk are harder. but still a great trophy
I can't say which is the most sought after. Again the Kudu might fall in this catagory. Most hunters who go over, especially for the first time have to take a Kudu. Now if you mean what is the most illusive, can't help you there. Someone more experienced than this one trip hunter will have to tell you that.
For me I had two "hardest" to get; the Steinbok and the Mountain Reedbuck.
We saw lots of animals but few good ones. We made several stalks on Steinbok but they never let us get close. After about a week of trying we finally got close enough to take this one with a Martini .218 Mashburn Bee.
My most favorite to hunt and the most difficult for me was the Mountain Reedbuck. If I get to go back, I will hunt Mt. Reedbuck again. We looked for this animal every time we went in the hills. We saw a lot of females and small males. Every group that saw us first spooked at long range. We had to spot them at long long range, glass them to see if a good one was present. We had to make a cautiousl stalk, keeping out of sight and watching the wind ever so carefully. One mistake on our part and they were gone. This animal was spotted very high up on a mountain, during a snow storm. We stalked for several hours and climbed 800 feet up to get it. This was tough on me as I was just 4 months out of knee suirgery. My PH is an archer and he got me with in 25 yards. I blew the heart and lungs out of this guy with a 200 gr. Nosler BT in a 338/308 and this animal just stood there. It looked around for us. You could tell he wanted us! It just wouldn't lay down and die. My PH cautioned me not to move, wait for it to go down. The PH said that if they felt threatened and cornered they would charge. It was something he had experienced with Archery hunters.