There is no such thing as an ideal diameter: It depends on what you're trying to do.

That said, sounds like you might like .6 mm based on what you said.

Layer adhesion should be fine with any. In theory, it should be better the thicker you go, but whenever you change nozzles, you need to readjust everything.

Personally, I just stick with .4 almost always because I'm lazy and it's an OK enough balance of detail and speed.

I love the look of 1mm and it's excellent for quick prototypes. Otherwise I pretty much stick to 0.4. I have multiple printers so I have different nozzles on different printers

I change nozzles depending on the project.

0.4 and 0.5 are nice for smaller parts with fine details. But for mineatures / small figures, I tend to 0.3 or even 0.2 nozzles. 0.1 only for exceptional small and detailled works, since these nozzles constantly tend to clogging. And then there are taller parts which have to be strong, like shelf brackets or vases. That's where my 0.8 and even 1.0 mm nozzles do shine.

Last, but not least: You don't need a high-flow hotend for wider nozzles. Any hotend will do (tested with an old Ender2), as long as you adjust speed and temperature accordingly. Some trial and error is the key.

Almost always 0.4 (sometimes 0.4 stainless). It is the biggest one that still gives me acceptable tolerances, and printing time is easier to deal with than imprecise parts.

Changing the nozzle and recalibrating feels like too much of a hassle for me, so I didn't experiment much though.

I like .6 for speed but there’s a lot of content out there saying how great .6 is and how you can’t really tell it apart. You absolutely can and arachne isn’t perfect either. If it’s a part that needs more strength I’ll go .6 but for anything else I’ll swap in my .4.

I have a Revo installed on my printer, so changing nozzles is easy. Since the nozzles are standardized and are the same height, I don't need to adjust the Z height.

If layer adhesion is a problem at larger sizes, check the line width, it should be larger than the nozzle size.

I haven't experienced layer adhesion dropping with higher nozzle sizes. Are you setting volumetric flow rate limits? If you don't limit the volumetric flow rate, and try to run higher nozzle diameters at the same speed as smaller ones (especially with greater layer heights), then this could cause that issue, because you're extruding material that isn't adequately melted. But in general, nozzle diameter and layer adhesion shouldn't be closely related.

Minimum feature size, on the other hand, is definitely related, and is indeed the main reason you might want a small nozzle or low layer height.

@x trench run You don't need to level the bed, but you do need to modify Z-height, and regrettably, in many printers' firmware, the z is adjusted along with the bed leveling.