Big decision, especially because you are starting fresh. Over the years, I have used several different brands. I also have been "trained" on the Jeti and CORE, somewhat. I would have to say, starting fresh, the programming would for me be equally as hard on all of them. But if one has had past experience with say Spektrum, then one would probably find that the transition to one of the others is a lot more challenging. Knowing what I know today, if I was starting over with a new brand, it would be the CORE, if I could afford it. However, the IX20 is a lot cheaper and Spektrum service is excellent. However, I have had Powerboxes for years and I know they have performed flawlessly. So, If I was to change brands now it would be CORE. If I was starting fresh, it would probably be the IX-20 and put the savings into something else for the plane(s).
When looking at Txers, also look at what is available for matching Rxers. Some brands have been out of stock for many months! Some RXer brands do not have the channels to even handle its Txer capability. And then there is the cost of the Rxers. Some brands are reasonable and others are not. If you are getting serious about jets, you will eventually want more than 14 channels. 9 channels just does not seem to do it anymore.