I can’t speak for Germany, but I guess that it won’t be much different than Denmark where my experience lies.

Almost all my recommendations has been mentioned before, but I’d like to point out:

• RS in my experience is reliable about 90% of the time. If you put in an order in can arrive in several shipments. I ordered 50 pieces of something got 46 from a UK warehouse and 4 from Germany. That’s another thing, some stuff ships from Frankfurt am Main, so no waiting for imports.
• Reichelt is good for cheap instruments. I’ve never used them for components, I prefer RS for that, but for instruments they carry some of the Chinese stuff that you can’t get other than on ebay or ali.
• Digikey stocks so much electronic components that sometimes you can’t avoid them. Where RS is really fast, their stock and prices are more suited for prototyping than production. Digikey is where you can get the specific series of cap and value you need for your repair project. Digikey will handle all the import and customs stuff as well.
• el-supply.com is new to the post. They’ve been in business since the 70s, but is primarily targeted towards Denmark. But they do have an international site. Some times they can be extremely cheap compared to RS and Digikey, especially with regards to stuff used for teaching electronics. I’ve been a customer since the late 90s privately, and I’ve placed several orders each year professionally since the early 10s as well. Never been let down.