The value of scripted monologues

[Solamnicknight]

My advice as a DM is do not script. Especially villain or antagonist lines, since more often than not a bad die roll or a player doing something unexpected like fireballing the villain in the middle of their grandiose speech is quite likely. As for NPCs the important thing is to figure out their personality, not exactly what they are going to say. It feels more immersive if you base what the NPC is saying on how the players are talking to the npc and how the npc would react to those interactions. For example, an arrogant and proud noble might be offended by brusque words or insults from the players, and might trade a few barbs back, but in a snarky implied insult sort of way. A military leader giving a speech before a big battle is going to gauge the reactions of his men, and may alter some things to get them even more fired up to take on their foes.