easiest more advance swappable?
There's a loaded question! If it's easy, it's not advanced.
I'm going to throw your question right back at you. What do you mean by "easy" and what do you mean by "advanced?" Do you want easy to build or easy to fly? Are you looking for a more complicated build, or something more challenging to fly?
Easy to build and fly, assuming one has already flown and has the basics down? Simple Scout, hands down. It is still the smoothest plane I have ever flown. I also outgrew it pretty quickly. It flies wonderfully. But that's it. If you just want to cruise around in the air, that's the bird for you.
How about the Mini Scout? Doesn't get much simpler to build, but it's really finicky about the build. It's gotta be right, or it just won't fly. Assuming the build is solid? That's a whole lot of fun in a little, tiny package! It's been made into a biplane, and there are a couple threads where we're just seeing how fast we can make it go. That little plane has amazing potential.
My Storch build has been put on hold, but I'm feeling the need to fly it more and more. Then there's the Spitfire!
Whootts! Not simple in any measure. But man, she is a blast to fly! I could go on and on.
What I'm asking is what do you WANT to fly, and what do you mean by easy and advanced?