Has Snowden provided some particular reasoning why Signal is better (and perhaps some others like Telegram might not be)?Your comment is wrong, plain and simple.
Telegram has a much larger user base than Signal and is therefore a much bigger threat to those governments and a number of countries have indeed blocked Signal, however it's still accessible in most of them due to Signal's censorship circumvention methods. Also I would argue that Snowden does indeed know a few things about how Signal and Telegram work considering, you know, him being Snowden.