The NPCs aren't really set up to give us much of a choice for subclasses. Lae'zel gives a choice between Battle Master and Eldritch Knight...but her Intelligence is only 11 (despite being a Githyanki). Astarion gives a choice between Arcane Trickster and Thief, but his Intelligence is only 9 (which is also bad for other reasons - rogues typically use Int for Investigation). Without a higher Intelligence, the spellcasting for both Eldritch Knight and Arcane Trickster is subpar, making it a poor choice.
