It depends on what you want to accomplish.
You can print MTG proxy cards at home, or by using a service such as MPC. If you print them at home, you shouldn’t expect to be able to recreate super high quality or realistic cards. That said, it’s very cheap to do so and may work perfectly fine for your purposes.
If you opt to print proxy cards through a 3rd party company, you can get a high quality result. However, it takes significantly more effort and time because you have to provide your own print files. Most companies also won’t print original art, so they won’t look realistic. Again, having a company print proxies for you can be a great way to get a bunch of casual playtesting cards.
Buying proxy cards is ideal if you are looking for high quality, realistic MTG cards. At Proxy King we try to make our proxies as realistic as possible. This lets you join games and play without people noticing you are running proxy cards in your Magic deck. We have created over 1,000 different MTG proxy cards that we print with high fidelity printers.