Warlock Mystic Arcanums

[ThirdProgenitor]

I'm playing a pact of the tome warlock with The fiend as my Patron and just hit lvl 11. So, I have absolutely no idea what i should take for my 11th lvl mystic arcanum... or my 13th, 15th or 17th. There are just too many good choices. Could i get some suggestions?

[Wyntonian]

What's your patron, pact and general sort of aesthetic? What sort of warlock are you playing, basically?

[Kane0]

Mass suggestion is fantastoc, thats what i use.

[ThirdProgenitor]

What's your patron, pact and general sort of aesthetic? What sort of warlock are you playing, basically?

Like I said, my pact is pact of the tome and my patron is the Fiend. I've been playing a mix of utility and aoe damage. I have hungar of hadar, fireball, poison spray and other such aoe spells as well as crown of madness, tongues, vampiric touch, Eyes of the rune keeper, banishment and other utility based spells like those.
As for aesthetic, im open to anything really. If it helps me optimize my build a little better, that's always good.

[JellyPooga]

It's a tricky question. You get to cast that spell once a day and you don't get to change it. Ever.

Conjure Fey is an absolutely solid choice; it's sheer versatility for giving you access to a variety of critters to choose from, most of which have their own spellcasting abilities, in addition to adding to your action economy, is pure gold. This would be my number one recommendation. On the other hand, it's not thematically appropriate for all builds.

Mass Suggestion is also a solid spell; useful in a variety of situations, but you might find it situational.

Circle of Death is a solid damage spell, but is indiscriminate; your fellow PC's will not likely enjoy it as much as you do!

The other choices are all fairly situational or limited in their own ways.

For higher levels, you have similar issues; Plane Shift at level 7 is great, but you aren't going to use it every day, same goes for Glibness at 8th or Imprisonment at 9th. I would tend towards the ones you're going to get the most out of; Forcecage or Ethearealness for 7th, Power Word: Stun or Demiplane for 8th and Foresight or True Polymorph for 9th.

[Kane0]

Forcecage is another arcanum i'd highly recommend.