Ugh too few knight crests and some are real hard to get.
There's enough to supply your main units with promotion items. Unless you're trying to use like... 20 people, they shouldn't be that big an issue.
Sety-Holsety, can use Rewarp staff from the get go...enough said
Sety comes so late he's hardly worth mentioning. Yeah, he has Holsety, but you can only use it for like... 2 chapters.
Asvel-Excaliber....100 hit, 40 crit...means bosses die in one round almost guaranteed.
I hate to sound nitpicky, but Asvel's personal weapon is "Grafcalibur". Excalibur is indeed in a lot of FE games, but FE5 isn't one of them.