Welcome to the forum!
Personally, I'm a Pioneer fan because I like their MCACC auto calibration better than Audyssey - almost exclusively because it can store more than one configuration (and I have three distinctly different listening positions).
I haven't used a modern Yamaha (my only one was a unit that I bought in 1997), so I can't speak to their new offerings. I did audition some last year from Denon (AVR-E400), Onkyo (TX-NR626), and Marantz (NR1504 and NR1604). The best bang-for-the-buck out of all of those was the Onkyo. Great power, more connections, better remote - just a good overall receiver. Those Marantz models have an outstanding form factor with the shorter chassis, but they don't have the power of the other two.
All of those receivers use the same Audyssey system, which isn't as advanced as the systems in the X3000 and X4000. That's one potentially big difference between the X3000 and the X4000 - the 4000 has Audyssey SubEQ for subwoofer equalization, and a more advanced Audyssey system overall. (EDIT - ADTG already posted that while I was typing.
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One reason to look at this year's offerings is HDMI 2.0, but that's only important if you are going to be passing 4K video through your receiver. The models that you're looking at from last year can pass 4K video, but not at as fast of a frame rate. For a lot of folks, that change won't be worth the extra money and they can save some cash buying last year's models.