Usually when the subject of quiet routers comes up on these forums, there will be a quick comment or two about the noise coming from a bit cutting wood, alum, or whatever. Usually bit noise will dominate the workshop, but if you often do more delicate cuts, or cuts in soft material like foam, then you may see some real benefit to having a quieter router motor. If you are getting an air cooled router, there’s no such thing as quiet. You’ll need watercooling if you hope to silence spindle noise much.
PWM control is something that I would leave off my list of requirements at this point, unless I had a very good reason to need it (for example, there’s just one digital out left on my controller for this). If you want speed control, you may want to look into getting a VFD spindle. Most of the good VFD spindles available with speed control are going to use a 0-10VDC signal for control, with some options also offering digital control with rs485. I also recommend watercooling. It is more expensive and complicated, but you can get the RPM much lower without overheating (and they’re a lot quieter than aircooled). I also recommend 220V for the same reasons, if you have that available and can wire it safely. If you go 120V just be sure to get no larger than 1800W… those 120V/2200W VFD’s and spindles are garbage.
I like my Huanyang 65mm watercooled 220VAC 1800W spindle, with 2200W Huanyang VFD. A few others on these forums use the same setup and like it as well. At first it seems like overkill spending so much on a “$500” cnc machine, but my machine shot well past $500 long ago lol. I occasionally do very long operations on aluminum, so having the low RPM and watercooling is great, especially when it gets to 100F in my garage. I’m controlling with RS485, since my 6-pack board has that option.