Tbh, Super may change people perception about Frieza.
If Super never existed and we purely based on DBZ story, then I would choose Cell over Frieza.
Both are great villain, tbh.
I still remember the tension in planet Namec that makes me chill almost every week.
But with Cell, the story were more unpredictable.
First we has Frieza come back and even bring his father along with him! On Earth.
Then, there is mysterious teenagers who looks like ordinary human with his long hairstyle but ended up become Super Saiyan - the feat that only achieved by Goku at that time!
Story goes to time travelling and human Android that seems like normal human. Goku and Vegeta already travel inter-planet and has face numerous villains from other planet.
This human enemy doesn't seems stronger than other extraterrestrial villain, right?
No! They turns out to be pretty invicible at that time.
And we dont not even move to the core of the story.
There is one mysterious Android in the future that longing to become greater fighter than previous human Android that we already think pretty invicible that time.
Just what kind of greater threat it will bring?
That triangle ugly face Android, what does he plan?
What really will happen after this?
And so on..
The build up and tension are great and that villain really give cunning yet upredictable move.
I have to admit that Goku fight on par with Perfect Cell in the tournament were not that great since I expect Cell to be stronger than Goku.
But what Cell has done and achieved before (and after it, as the story progressed), coupled with story building around him made me put him slightly > Frieza.
Definitely if we including Super, Frieza would be more interesting character since he get more development than Cell that really looks like "your generic villain" in Super.
But if we limiting the scope to DBZ's story only, then I would pick Cell slightly over Frieza.
Thats my two cents! ✌️