I have the HK 235 and am pretty happy with it so far. The 235 has EZSet, the 335 has EZSet+. The difference isn't too much tho, the 235 just adjusts the speaker levels, while the 335 will do that plus measure the speakers distances, sizes, and crossover. Still no eq. The only other differences between the 2 is that the 335 has a little more power and is able to run speakers in a second zone, and has an extra remote for that zone. Not sure if that is something you need or not. I find the 235 has more than enough power, and I was on a strict budget so could not go to a more expensive receiver at the time, and my requirements were pretty basic. The only problem I have had with the 235 is that it will go into protect mode at -10db when listening to music thru stereo. The receiver isn't hot, so I am thinking it is has to do with my speakers, which are 6 ohm. I was pushing the receiver when this happened, -10db is not a normal listening volume that I would use, and have not had a problem with it while listening to dvds.
My familiarity with Yamaha's are limited, but I did try out a HTR5790, the equivalent to an RXV1400, the previous model to the 1500. Having the auto eq is a nice feature. Other features that may or may not be necessary for you is I believe 3 component inputs, and the ability to upconvert s-video and composite thru the component output so you only need one connection to your tv from the receiver. The 1500 will also have more options for DSPs if you like to use those. For me those things were not a necessity, so you will have to decide what you prefer, but like I said the auto-eq would be nice.
As far as direct comparisons, don't worry about the lower wattage ratings on the HK, it will easy have as much power or more than the 1500 in 5.1 or 7.1. For music listening in stereo the 1500 may have an advantage there. I was not able to compare the receivers back to back, but from what I remember the 5790 seemed brighter, or emphasized the higher frequencies more while the HK's I had were warmer, or emphasized the lower frequencies. The HKs got more bass out of my towers than I what I was used to with my old receiver (Pioneer 509s). If you have an opportunity to demo either receiver with your speakers it is strongly encouraged.
I will leave it at that, but if you have any questions let me know and I will try to answer.
