Diddy is a lot like Snake from what I have played. Diddy is narrow minded when it comes to banana play. You can throw a banana at lower skill levels and it works like a charm. Running up with grabs afterwards is pretty hilarious. However, upper level I would say is nothign like that. Diddy requires having a sense of stage control to use properly. Diddy works not only with his own moveset, but also with what the other character has along with banana dynamics. None of it really requires a lot of proper timing, fancy movement inputs, but it requires some good mind power to process everything that is happening. In the end, Diddy is all about character familiarity in my opinion. A lot like snake. After playing snake for a long time, you just know when his nades are scary and when they are not.
Falco I feel is not tech savvy at all either, nor does he really require a lot of player familiarity to get down fairly well. Falco is all about knowing what your moves do and merely mixing them up in different ways. You can play falco pretty solidly if you do nothing more than camp, phantasm, jab, grab, and ftilt. One can include his BPG, gatling combo, phantasm cancels, and other technical stuff, but his basics make the core of his game. That is what makes him good, and in the end what really matters most.
Overall, I would not say either is rather more technical than the other. They each have there small technical aspects like glide tossing, or SHL timing. The major differences is that Diddy requires being able to juggle in and out of a lot of random situations on the fly while Falco requires you to have the ability to apply simple tools effectively and mix them up. In this regard, I find diddy more difficult to use than falco.