Easiest air layer, and the one i do most often is by far lychee. Rambutan and pulasan are also very easy to air layer. (Morton says in her book that rambutan air layers don't grow when planted out, and some other authors have repeated her statements, but this is not correct. Maybe it doesn't work well in Florida limestone.) Longan can also be air layered but is not as easy as the cut often bridges and heals itself. But air layering is traditional way to propagate longans. I also air layer acerola (barbados cherry). Can be done by cuttings but success rate is much higher with air layers. I've also done miracle fruit but takes a very long time. Same with chico (sapodilla). I've tried jaboticaba air layers with no success. Also tried durian with no success, although i've heard others have been succesful with durian. One that i want to try that i heard air layers well is nutmeg, that way you know which plants are male and which female and can plant the right combo.
General rules of thumb are that plants that start from cuttings will definitely air layer (though not always vice versa). Also that most hardwood trees air layer well.
Oscar