I very much agree with what @headingnorth already wrote. Altcoins aren't bad per se, but you should really understand what you're investing in. I'm not against altcoins but I think for conservative-leaning or inexperienced investors Bitcoin is much better.
Here's a list of arguments I know which hint to a superiority of Bitcoin versus most (>90%) of all altcoins:
1) PoW/PoS Security: In the case of PoW altcoins, the difference in security between Bitcoin and even its nearest competitor (Litecoin/Dogecoin, which are merged mined, so they are "symbiotic" in some way) is already very big (factor 50). In the case of PoS, the model is not 100% proven and is perhaps vulnerable to identity theft-based attacks due to its "
weak subjectivity" approach (the "ask a friend for the best chain" principle).
2) Human mind: There will not be 100+ altcoins with a similar adoption level than Bitcoin, because there will always be less than 10 recognized by the common human being, due to limitations of our memory. No one can remember 100 different brands of the same product (or very few people can).
3) Lack of long-term growth: There are only two altcoins, Ethereum and Ripple (XRP), which had a long term growth similar in the order of magnitude than Bitcoin. Both have centralization problems. Litecoin and Monero are two examples of relatively successful altcoins which are even older, but their ROI (e.g. if we compare the price 2015 and 2024) was much lower than Bitcoin's. Most altcoins tend instead to lose steam after a few years of growth and then end up as almost dead low-caps (examples: BitShares, NEM, Nxt ...).
4) Centralization: Linked to the first argument. 90% of all altcoins are premined, enabling the founders to manipulate its consensus in many cases (e.g. threatening to sell if they don't like an upgrade by an independent developer).
5) Risk of technobabble scams: In the case of smaller altcoins, many try to sell their "technology" aggressively as something groundbreaking, but the fact is that there have been only few real technological breakthroughs in the altcoin sector (examples being XRP, Grin and perhaps Ethereum). The problem with "AI coins" which don't need blockchains to work, which was already mentioned in the thread, is related to that issue.
6) Most altcoins don't solve real-world problems: Even Ethereum struggles to justify its smart contract feature. There are very few killer apps, most of the dApp stuff is DeFi circlejerk aimed to traders ("trade a DEX token on another DEX"
). Tokens and even simple DEXes can also be realized with Bitcoin Script.