Hellish Rebuke as Paladin?

I play a tiefling paladin. Have Hellish rebuke, love it, how do I get it as an actual multiple per day thing (Currently 1/day as tiefling.)

I take it you're playing with 2014 rules?  Some GMs will allow characters to use regular spell slots for their innate spells (since later books like Mordenkeinen's Monsters of the Multiverse did that with all its PC options), otherwise it looks like you're going to need to multiclass.

Oathbreaker Paladins also get Hellish Rebuke as part of their Oathbreaker Spells feature.

If you are playing under 2014 rules,  you could take the Magic Initiate feat and choose Warlock as the spell list from which you learn your chosen spells. 

Otherwise, you will need to take at least 1 level in Warlock, as I believe those are the only ways to get Hellish Rebuke.

Magic Initiate under 2014 rules only lets you cast the spell once per day.

Quote from 6thLyranGuard >>

Magic Initiate under 2014 rules only lets you cast the spell once per day.

 So it does. I stand corrected. That leaves taking a level of Warlock or taking Oathbreaker as a subclass.

I mean, no offense, but are you sure that you want to?

Hellish Rebuke on most of the sites I read say it’s a pretty underwhelming spell, especially since it does fire damage (the most common and resisted type in the game). Don’t get me wrong; I love the concept, and if that is what you’re going for, than more power to you.

Quote from Actionsparda >>

I mean, no offense, but are you sure that you want to?

Hellish Rebuke on most of the sites I read say it’s a pretty underwhelming spell, especially since it does fire damage (the most common and resisted type in the game). Don’t get me wrong; I love the concept, and if that is what you’re going for, than more power to you.

 It does more damage than any smite, and it's functionally free, unless you've got other reaction abilities, or you're running out of spells a lot. (Opportunity attacks just don't happen often enough to reserve one's reaction for them. If you think you're gonna want the OA more, you just don't rebuke.)

And, while it does have an opportunity cost, in that you're taking the spell instead of something else, it's probably lower for a front-line fighter type than it is for most.

I'm sure that various people on the internet say it's not that good, and they may be right on their terms, but their terms are not OP's terms, and "this is fun" is way more important than "this is theoretically optimal".

So for a fighter 1/warlock X (Pact of the Blade) with three level 1 spells let’s say, should I consider hellish rebuke over spells like armor of agethys, hex or Tasha’s Hideous Laughter?