Flysky FSI6 is good, it can do differential thrust but it uses up nearly all the mixes available so doing that and flaperons together is tricky. You can also use preprogrammed mixers that go in the wires from receiver to servos to do extra mixes so it’s limited number of mixes is less of a problem. You can make it 10 channels as well.
If you want unlimited mixes you need OpenTX, the Jumper T12 Pro is the best sub $100 open TX radio but it’s more complex to learn OpenTX than simpler radios like the Flysky.
I love the Spektrum Dx6 lineup. I have the dx6i, dx6e, and dx6. For personal everyday use I use the dx6 but I’d say the best value is the dx6e. It can do most the things my dx6 can do and is a bit cheaper. The dx6i is a good budget option and can do a lot of things as well but the screen is harder to see, and it only has 10 model memory. You can usually find them on eBay for under $100 though which makes them a great affordable option.
Spektrum is fine if you want to be limited in your number of channels and be only using DSMX receivers or Horizon Hobby BNF planes. You don’t need it to fly, a cheap TX like the Flysky wil do everything you need.
An OpenTX radio will do far more if you are prepared to learn. There’s a few good second hand Taranis 9XD or QXY radios around, all for much less than the price of a new DX6E.
I bought 2 Flysky fs-i6x transmitters when I started, so I could buddy box with them. They're pretty good so far and I haven't found any limitations. The menu takes a bit of getting used to as the buttons are counter intuitive. Long press cancel is actually the confirm option for example. But it's fine once you're used to it.
I had been looking at mixes recently, and it only has 3 available, so that might be a limiting factor as things get more advanced. So you might want to consider whether you buy something affordable just now, knowing you might need to upgrade later, or spend a bit more now on something that will last you a lot longer.
I like the look of that Jumper tx. I think that would be my next upgrade choice.
As I said about mixes, the use of a fixed mixer box will give you extra mixes for free with no programming. Being able to go to 10 channels is another bonus. Many more expensive TX’s limit the number of mixes as well.
I should give the X9 Lite an honourable mention for under $90 OpenTX transmitters too, but the Jumper T12 pro does everything it does and has internal multi protocol for only $15-20 more.
Spektrum. I have collected three DX6e a DX6i two DXe and a Dx4 plus a DX7 which I use for buddy Box. Never intended to get this many but I found them on craigs List and Garage Sales. Great xmitters. But buy the model with the most channels you can afford.
I see it now, I just looked it up. I didn't know they made one. I have both the i6X and the I6S. The S is lousy because you have to look down at the display and go into it to set the trim. there is no way to do that while the plane is in the air.