There are already a lot of coins that we can use if the issue is network congestion or high fees really. I hardly doubt these coins would be replaced unless some really good altcoin suddenly pops out or said coins were to go out due to some bad business models they're going to adopt. I've used Matic, SOL, Litecoin, BNB, and a few others before for transfers and I've never had any big issues with them before. As for "best", I don't think there's a single best one out of all, it's a matter of preference among those that can be described as good alternatives instead.

As for altcoins that are overlooked in general, well, that can't be helped. Marketing is one thing that is needed and if they can't properly push for it, any coin, no matter how good, would inevitably stay dead especially if you consider how the altcoin scene is already full of hundreds of coins itself.