I have a sorlock, 4/4. I get a feat now, and I am thinking Tasha's Eldritch adept to get an extra invocation, along with another at 5th level.

Currently I have Agonizing Blast and Voice of the Chain Master. I want my blasts to be more useful...I have Quicken Spell as a sorcerer so I can occasionally unleash a barrage of 4 blasts per round. We just went up to 8th level but have as few weeks off due to the holiday.

So what would you take?

I would take repelling blast.  It can be used to break a grapple and a host of other things.  It also can be added on each blast.

Repelling Blast and Lance of Lethargy each have their uses, but it is my opinion that Repelling Blast has more. Lance of Lethargy can control how much a creature moves in any direction, sure, but Repelling Blast can push, and pushing is useful for a number of reasons:

• Breaking melee so you can avoid an opportunity attack when running away
• Pushing off a cliff/into dangerous zone
• Breaking grapple
• Pushing the creature into a place where it can be reached by a melee attacker, when it could not be if not pushed (i.e. fighter 40 feet away from target)

All while Lance of Lethargy only reduces the creature’s ability to maneuver the battlefield.

EDIT: Somehow forgot this thread wasn’t specifically about a debate between the two. Sorry

If it were per ray, so with 4 blasts you could reduce move by 40 its pretty close but I'd still say pushing in a white room. The issue is you have to think about how your DM creates battlefields. If you are in smallish enclosed spaces then there will be many times where you can't push them the full 40, how many cliffs does he give you to push people off, does he grapple etc so you might not be pushing them enough to avoid retaliation or getting many extra bonuses from shoves. If you can reduce their speed by 40 which sadly lance of lethargy can't to as its per attack not per ray(so 20 when quickened for 2 eldritch blasts) you can stop almost any melee attacker from being able to get into melee. Which in tight quarters may prove more useful in the long run.

It's worth noting that lance of lethargy is only once on each of your turns, whereas repelling blast doesn't have a limit. So a high level warlock casting eldritch blast could push a creature up to 40 ft., but could only slow that creature by 10 ft.

Nothing says you can't get both, though.

If you or your party members are casting area control spells (Hunger of Hadar, Spike Growth, Wall of Fire, etc...) then Repelling Blast is excellent. If they run out of the area, you push them back in.

Spike Growth and Repelling Blast are a cheese grater. The druid in my group and my fiendlock ruined a Cloud Giant with this combo. Druids and Warlocks have a lot of great combinations to work with.

Anyway, I'd vote for Repelling Blast.

I'm currently playing a level 7 fathomless warlock with both repelling blast and lance of lethargy. My go-to combat loop is tentacle of the deeps, summon shadowspawn (despair form), and eldritch blast. I can push the enemy 20 ft. away and slow them by 40 ft., effectively shutting down their ability to move into attack range. We have a cleric in the party with spirit guardians, which halves movement and deals damage "when the creature enters the area for the first time on a turn or starts its turn there," so I can push an enemy into the area to proc the damage and kill their movement so they're stuck inside the area.

Overall I'd say repelling blast is the more effective invocation of the two, but combining them both and then stacking other effects on top can be absolutely devastating.

Quote from LurkyTheHatMan >>

Quote from temery2383 >>

I'm currently playing a level 7 fathomless warlock with both repelling blast and lance of lethargy. My go-to combat loop is tentacle of the deeps, summon shadowspawn (despair form), and eldritch blast. I can push the enemy 20 ft. away and slow them by 40 ft., effectively shutting down their ability to move into attack range. We have a cleric in the party with spirit guardians, which halves movement and deals damage "when the creature enters the area for the first time on a turn or starts its turn there," so I can push an enemy into the area to proc the damage and kill their movement so they're stuck inside the area.

Overall I'd say repelling blast is the more effective invocation of the two, but combining them both and then stacking other effects on top can be absolutely devastating.

 

 How are you slowing them 40ft? Despair Shadowspawn slows for 20ft and Lance of lethargy slows for 10ft, regardless of beams, so you'd only get 30ft of slowing. Which is still enough to reduce most humanoids to 0ft for their next turn.

 The tentacle slows as well.

Quote from LurkyTheHatMan >>

Quote from temery2383 >>

I'm currently playing a level 7 fathomless warlock with both repelling blast and lance of lethargy. My go-to combat loop is tentacle of the deeps, summon shadowspawn (despair form), and eldritch blast. I can push the enemy 20 ft. away and slow them by 40 ft., effectively shutting down their ability to move into attack range. We have a cleric in the party with spirit guardians, which halves movement and deals damage "when the creature enters the area for the first time on a turn or starts its turn there," so I can push an enemy into the area to proc the damage and kill their movement so they're stuck inside the area.

Overall I'd say repelling blast is the more effective invocation of the two, but combining them both and then stacking other effects on top can be absolutely devastating.

 

 How are you slowing them 40ft? Despair Shadowspawn slows for 20ft and Lance of lethargy slows for 10ft, regardless of beams, so you'd only get 30ft of slowing. Which is still enough to reduce most humanoids to 0ft for their next turn.

• Tentacle of the deeps: -10 ft.
• Lance of lethargy: -10 ft.
• Summon shadowspawn: -20 ft.

Update. I have used repelling blast to great effect. I kept a mage from casting spells for an entire fight because I kept pushing him into a pit. This is REALLY useful!