Any software is going to take getting used to. For me, the phpBB framework is fairly familiar, but only because I've been working with it almost exclusively for a few years (aside from a few other projects). So if I were to answer your questions, I would probably say "Yes, phpBB development is mostly pretty easy." That would be a true statement for me, but it is subjective.
Ultimately, it will come down to whichever framework you end up using; as you work with it you will learn more and more about it and it will come more naturally to you, and at that point you will probably call it "easy".
Your question is asking which of SMF, MyBB, and phpBB is the easiest to develop with, and I'd suggest you take a look at each one to see which looks easiest to you.
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