To me the biggest difference is how bitcoins are created. It takes a great deal of investment in money, time, effort, and energy just to mine and produce a single bitcoin.
Unlike altcoins, you can't just print a bitcoin out of thin air whenever you want. Any idiot with a PC can create a new crypto altcoin and print an unlimited or nearly unlimited supply for himself to dump onto the market, whenever he wants. But that's not how bitcoin works.
Imagine having a money printer that prints an endless amount of dollars anytime you want. You don't have to do shit to earn it. Just press the print button and enter the amount you want. That's basically how garbage like dogecoin, ethereum, solana, fartcoin, pepecoin, clowncoin, etc. all work. They are just a digital recreation of the unlimited fiat money system but even worse, with zero discernible value beyond being a Ponzi scheme.
What are other big differences?

Bitcoin mining facility