3D Printing

Prusa is top of the line for open source and very much falls into "works out of the box". The other bed-slinger style printers like Ender are cheap but tend to have issues and are a money-sink for upgrades to get them working (lots of mods there). If you're into hacking and modding stuff though, look into Voron printers. I'm not sure if any of the Voron versions fall into your budget, but you can buy a kit or do open-source. They're self-built, extremely fast, customizable, and really meant for the people in the printing community who like to program and mod things.

I got a Prusa (MK2s) six years ago and it's been really, really great. Unfortunately, your budget restriction rules out the current model.

If you can get access to a printer at a friend's house, a library, a school, a workplace, a makerspace, etc., I would suggest not buying a printer while totally new to 3D printing. Do some 3D printing for awhile. Then, on the basis of that experience, decide if you want to commit to having a good printer at a slightly higher price point.

400€ is really very restrictive. Commercial 3D printers are 10,000€ to 100,000€. Prusa's printers are extremely good for their modest ~900€ price.

If you do decide to get a Prusa, I recommend the kit over the assembled option. It's cheaper, and the familiarity you get with its components and construction during assembly gives you the power of fearless repair and tinkering -- you've already assembled it once, so disassembling it and reassembling it for repair or upgrade is no big deal.

I bought an Artillery 3d Genius, after owning an Ender 3 for 4 years. It has worked flawlessly out of the box, while I needed to tinker with the Ender endlessly.

There is a 3d printing discord, that has an often updated flow chart. Assuming you dont want resin, the choice is mostly based on how big you want to print + budget:

• <200m^3: Kingroon KP3S ($170) or Prusa mini+ ($460)
• <300m^3: Artillery Hornet ($170), Sovol SV06 ($300), Prusa MK3S ($800-$1100)
• 300m^3+: Sovol SV03 ($400), Ultimaker S3 ($5k)

I actually had a pretty good experience with my Ender 3 V2. A lot of the cheap printers (including the Enders) work just fine out of the box, but you have to temper your expectations as a beginner. Don't expect a 2D printer experience from a 3D printer. Even the more expensive machines require some maintenance and tuning from time to time. Most printers are going to require at minimum some bed leveling and minor calibration to be running the way they should (tweaking flow rates, calculating e-steps, etc). The Bambu printers look to be some of the most ready out-of-the-box printers, but even they are going to need some maintenance from time to time. There are a lot of consumable parts in 3D printers that need changing out from time to time (nozzles, thermistors, heater cartridges, etc). Some printers make that easier, but it's not fool proof. As a beginner, I'd honestly recommend getting a cheaper bed slinger to learn the ropes. Learning to troubleshoot on a cheaper printer with inexpensive replacement parts can be a good thing Make sure to get something that's new and not used starting out (unless you are into some major troubleshooting). You also probably stand to benefit from one of the more popular printers with a strong online support community as most problems will have been encountered by someone already. Hopefully that's helpful. Good luck if you decide to jump in!

I was in a similar position recently, but also valued OpenSource (see meel being here ;) )

I went with the Prusa Mini+ semi assembled kit.
it's been chugging through filament for a few months.

There is the Sovol SV07 for about 300€-ish. It comes with Klipper and should check all your boxes. I bought the SV06 Plus two months ago it works OK. You have to tighten all the screws and actually read the manual, but that's it. If you want a guaranteed problem free OOTB experience, you have to buy Prusa (top quality control and software) or Bambulab (not really hackable but runs well) for 600-800€.