I assume you ask about FDM printers, as these are the most common and attainable type. Here's the essence of what I learned about it.
FDM 3d printed parts can already be found in many public places where they often appear almost indistinguishable from "normal" plastic parts.
Your results can be exquisite, given these three prerequisites:
- Suitable design. For example, and most importantly: FDM print quality looks somewhat ugly on the underside of overhangs, even if you help it with support material. For nice results you need to already take this into account when designing your casing.
- Well adjusted printer. A perfectly tuned 3d printer (using filament with a constant diameter) can produce very smooth surfaces without ugly artifacts (up to a certain print speed/acceleration), with each and every print. The cheaper the printer, the harder it is to reach and maintain that state.
- Right material. Skip PLA, use PETG or better instead. PLA is brittle, hard to sand, and exhibits significant creep under load. Heat deflection can quickly become an issue (limit for PLA is ~60°C). Also, the color of the material can change the quality impression of your parts a lot, just by hiding or highlighting layer lines and imperfections.
From my 8 years of experience, an original Prusa MK3S printer is the way to go. You can get good results with cheaper printers too (Ender 3 for example), but usually not as good, and you will need to invest a lot more time (easily one day per month) adjusting (to) your printer, upgrading, fixing and adjusting your slicing profiles, or worrying over failed prints. Especially for a newbie, a Prusa will make your life much easier, because it's a perfect well rounded and supported product that just works. If you are on a budget, look for a used machine. I got my first MK3S used and never regretted it. Good luck!