Would you lease this horse in my case?

It really depends on what you want to do with riding. If you are interested in showing and doing well, I'd go with the QH. If you are more interested in the training aspect of riding the first horse sounds like a good match. It can be disapointing to work with a horse that you know is up for sale though. Whatever you accomplish, she'll still be leaving at the end of the year (or sooner) and you'll be left without a horse. Just something to consider.