My (Terrible) Nozzle Experience
Over the years I've been the beneficiary here. Finally I have something of value to contribute.
TLDR: Don't buy cheap nozzles, they're not worth your time.
About 8 mths ago I started a project requiring large parts (nearly the full print volume of the mk3s). I wanted to get these done in a reasonable time and they didn't need to be incredibly precise, so I decided to get a 0.8 nozzle. I ended up buying a whole set of nozzles from 0.2 to 1mm for like 10 bucks shipped on ebay. Like most, I print nearly everything in PLA, but these parts were going to be outdoors and subject to a bit of stress - so I went with PETG. It was my first time changing nozzles, so I was extremely careful, followed the instructions to a tee, and recalibrated everything. The prints weren't great from the start, but with a bit of fine tuning in slicer I was able to get stuff that looked ok, just with what looked to be a really under extruded first layer (not really a problem with PETG as it adheres to the smooth plate so well).
So, printed my project in PETG and then switched back to PLA, and changed the nozzle down to 0.6mm, since there's a lot of talk that you can get similar results to 0.4 but in half the time. Try as I might I couldn't get a good first layer with PLA and 0.6 nozzle. Here starts weeks of frustrations. One brand of PLA was bubbling a bit as it extruded, another was just completely stopping and starting. Both had terrible adhesion. I tried tuning the temps and flow on the printer as it printed, and got better results with lower temps and 120% flow.. but it still looked under extruded or high (I enough to know it wasn't actually too high).
After a whole morning of trying to track this down, I thought I'd switch the nozzle back to the original E3D v6 0.4 nozzle that came with the machine and has printed well over 10kg of PLA. I recalibrated everything and got a good first layer cal on my second try. Started up a print I needed done with some fine detail on the first layer and tuned the Live Z while it was printing - everything is perfect. Really good quality print.
So please, do yourself a favour and DON'T save money on nozzles!
RE: My (Terrible) Nozzle Experience
If you are talking standard brass e3d nozzles are by far the best, and not expensive unless you are buying the premium versions.
If you do want to save a little money a lot of resellers offers discounts if you buy a few together.
Mircoswiss, Brozzl, Bondtech all do pretty decent v6 nozzles that will work well on the MK3 and later variants. I find the MicroSwiss Twinclad XT to be my go to nozzle, but I also like the e3d copper nozzle a great deal.
The only cheap ones I've found to be consistent are Trianglelab on Aliexpress but these days they are not much cheaper than buying e3d nozzles.
ObXidian nozzle by e3d is a very good option if you want something long lasting. I've had a full year out of the original version of e3d's Nozzle X too.