I've only had one of each, the Keemun Encore (higher end) and the Assam Melody (lower end).
I absolutely love the Encore, a Hao Ya A. Has all the good things I'd expect from a Keemun, ie that rich complex biscuity aroma with that Burgandy character. I will probably order more when its back in stock.
I wasn't so impressed with the Assam Melody. It was very one-note, heavily malty and that's all. I used most of this as a base to some rosemary iced tea I made and it was delicious that way. Otherwise I would not drink it straight.
If you have to try just one kind of each, I'd suggest the Keemun Encore and the Assam Harmony. But why not get a sample of each?